Xcode: Use explicitFileType to mark source types (#14093)

Replace use of lastKnownFileType with explicitFileType to insist
that Xcode treat the file as we ask.
CMake Nightly Date Stamp
FindOpenGL: simplify OS selection code

This was using nested if's, now it uses elseif to flatten that. It also removes
one "if" from the general "else" branch that checks for Apple, as that has it's
own branch anyway and can't be true at this point.
FindOpenGL: require headers to be found on non-Windows platforms (#13746)
Merge topic 'OpenGL-require-includes' into next

5be3593 FindOpenGL: require headers to be found on non-Windows platforms (#13746)
b10a171 FindOpenGL: simplify OS selection code
f2958ff CMake Nightly Date Stamp
make CUDA_COMPUTE_BUILD_PATH use relative paths to binary dir.

make CUDA_COMPUTE_BUILD_PATH use a relative path to the current
binary directory instead of the current source directory if the source
file considered is in the current binary directory. This is done to
shorten the paths given to the compiler.
Merge topic 'xcode-explicitFileType' into next

5683146 Xcode: Use explicitFileType to mark source types (#14093)
Merge topic 'cuda_compute_build_path' into next

2d8355b make CUDA_COMPUTE_BUILD_PATH use relative paths to binary dir.
Merge topic 'fix-clear-INCLUDE_DIRECTORIES-prop'

5a5e0fa Fix clearing of the INCLUDE_DIRECTORIES DIRECTORY property.
Merge topic 'missing-fclose-in-trycompile'

ce441fa try_compile: add missing fclose() to recently added error case
Merge topic 'doc-get_filename_component'

df71f96 get_filename_component: Document path components more clearly (#14091)
Merge branch 'master' into next