Repository: pytorch
Issue: omp.h not found on macOS during install from source at github repo
Labels: module: build,triaged,module: macos

### 🐛 Describe the bug


Following the build instructions at https://github.com/pytorch/pytorch#from-source
Sadly I am getting an error at this step:
```
export CMAKE_PREFIX_PATH=${CONDA_PREFIX:-"$(dirname $(which conda))/../"}
python setup.py develop
```

   "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-macosx14.0.0 -Wundef-prefix=TARGET_OS_ -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name OpenMPTryFlag.cpp -mrelocation-model pic -pic-level 2 -mframe-pointer=non-leaf -fno-strict-return -ffp-contract=on -fno-rounding-math -funwind-tables=1 -fobjc-msgsend-selector-stubs -target-sdk-version=14.4 -fvisibility-inlines-hidden-static-local-var -target-cpu apple-m1 -target-feature +v8.5a -target-feature +crc -target-feature +lse -target-feature +rdm -target-feature +crypto -target-feature +dotprod -target-feature +fp-armv8 -target-feature +neon -target-feature +fp16fml -target-feature +ras -target-feature +rcpc -target-feature +zcm -target-feature +zcz -target-feature +fullfp16 -target-feature +sm4 -target-feature +sha3 -target-feature +sha2 -target-feature +aes -target-abi darwinpcs -debugger-tuning=lldb -target-linker-version 1053.12 -v -fcoverage-compilation-dir=/Users/mikekg/pytorch/pytorch/build/CMakeFiles/CMakeTmp -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0 -dependency-file CMakeFiles/cmTC_60615.dir/OpenMPTryFlag.cpp.o.d -skip-unused-modulemap-deps -MT CMakeFiles/cmTC_60615.dir/OpenMPTryFlag.cpp.o -sys-header-deps -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk -D USE_PTHREADPOOL -fopenmp -internal-isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/usr/include/c++/v1 -internal-isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/usr/local/include -internal-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/usr/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include -Wno-reorder-init-list -Wno-implicit-int-float-conversion -Wno-c99-designator -Wno-final-dtor-non-final-class -Wno-extra-semi-stmt -Wno-misleading-indentation -Wno-quoted-include-in-framework-header -Wno-implicit-fallthrough -Wno-enum-enum-conversion -Wno-enum-float-conversion -Wno-elaborated-enum-base -Wno-reserved-identifier -Wno-gnu-folding-constant -std=gnu++17 -fdeprecated-macro -fdebug-compilation-dir=/Users/mikekg/pytorch/pytorch/build/CMakeFiles/CMakeTmp -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 1 -fstack-check -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fno-cxx-modules -fcxx-exceptions -fexceptions -fmax-type-align=16 -fcommon -clang-vendor-feature=+disableNonDependentMemberExprInCurrentInstantiation -fno-odr-hash-protocols -clang-vendor-feature=+enableAggressiveVLAFolding -clang-vendor-feature=+revert09abecef7bbf -clang-vendor-feature=+thisNoAlignAttr -clang-vendor-feature=+thisNoNullAttr -mllvm -disable-aligned-alloc-awareness=1 -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o CMakeFiles/cmTC_60615.dir/OpenMPTryFlag.cpp.o -x c++ /Users/mikekg/pytorch/pytorch/build/CMakeFiles/FindOpenMP/OpenMPTryFlag.cpp

  clang -cc1 version 15.0.0 (clang-1500.3.9.4) default target
  arm64-apple-darwin23.4.0

  ignoring nonexistent directory
  "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/usr/local/include"


  ignoring nonexistent directory
  "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/Library/Frameworks"


  #include "..." search starts here:

  #include <...> search starts here:

   /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/usr/include/c++/v1
   /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/include
   /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/usr/include
   /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
   /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.4.sdk/System/Library/Frameworks (framework directory)

  End of search list.


  /Users/mikekg/pytorch/pytorch/build/CMakeFiles/FindOpenMP/OpenMPTryFlag.cpp:2:10:
  fatal error: 'omp.h' file not found

  #include <omp.h>

           ^~~~~~~

  1 error generated.

  ninja: build stopped: subcommand failed.



Call Stack (most recent call first):
  cmake/Modules/FindOpenMP.cmake:506 (_OPENMP_GET_FLAGS)
  cmake/Dependencies.cmake:1198 (include)
  CMakeLists.txt:760 (include)




### Versions


(py311) mikekg@mikekg-mbp pytorch % python collect_env.py 
Collecting environment information...
PyTorch version: N/A
Is debug build: N/A
CUDA used to build PyTorch: N/A
ROCM used to build PyTorch: N/A

OS: macOS 14.4.1 (arm64)
GCC version: Could not collect
Clang version: 15.0.0 (clang-1500.3.9.4)
CMake version: version 3.29.2
Libc version: N/A

Python version: 3.11.8 (main, Feb 26 2024, 15:36:12) [Clang 14.0.6 ] (64-bit runtime)
Python platform: macOS-14.4.1-arm64-arm-64bit
Is CUDA available: N/A
CUDA runtime version: Could not collect
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: Could not collect
Nvidia driver version: Could not collect
cuDNN version: Could not collect
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: N/A

CPU:
Apple M1 Max

Versions of relevant libraries:
[pip3] executorch==0.2.1.dev0+unknown
[pip3] flake8==6.0.0
[pip3] flake8-breakpoint==1.1.0
[pip3] flake8-bugbear==23.6.5
[pip3] flake8-comprehensions==3.12.0
[pip3] flake8-plugin-utils==1.3.3
[pip3] flake8-pyi==23.5.0
[pip3] mypy-extensions==1.0.0
[pip3] numpy==1.26.4
[pip3] optree==0.10.0
[pip3] torch==2.4.0.dev20240422
[pip3] torchao==0.1
[pip3] torchaudio==2.2.0.dev20240422
[pip3] torchsr==1.0.4
[pip3] torchvision==0.19.0.dev20240422
[conda] executorch                0.2.1.dev0+unknown          pypi_0    pypi
[conda] numpy                     1.26.4                   pypi_0    pypi
[conda] optree                    0.10.0                   pypi_0    pypi
[conda] torch                     2.4.0.dev20240422          pypi_0    pypi
[conda] torchao                   0.1                      pypi_0    pypi
[conda] torchaudio                2.2.0.dev20240422          pypi_0    pypi
[conda] torchfix                  0.1.1                    pypi_0    pypi
[conda] torchsr                   1.0.4                    pypi_0    pypi
[conda] torchvision               0.19.0.dev20240422          pypi_0    pypi

cc @malfet @seemethere @albanD