Xcode: Generate per-target file references (#15111)

Xcode requires a separate PBXFileReference for each target source group
that references a source file.  Xcode 6 now diagnoses re-use of the same
PBXFileReference from multiple source groups.  Add the referencing
target name to our internal map key so we use a per-target reference.
Merge branch 'backport-xcode-duplicate-file-refs' into release
Merge branch 'backport-xcode-duplicate-file-refs' into xcode-duplicate-file-refs

Resolve conflicts in Source/cmGlobalXCodeGenerator.cxx in favor of our
side.
CMake Nightly Date Stamp
Help: Add notes for topic 'InstallRequiredSystemLibraries-vs-openmp'
Merge topic 'InstallRequiredSystemLibraries-vs-openmp' into next

d538c55e Help: Add notes for topic 'InstallRequiredSystemLibraries-vs-openmp'
Merge topic 'xcode-duplicate-file-refs' into next

d73f8828 Merge branch 'backport-xcode-duplicate-file-refs' into xcode-duplicate-file-refs
e7114226 Xcode: Generate per-target file references (#15111)
Merge topic 'wix-log-on-failure'

4952030c CPackWiX: Attach wix.log on test failure.
Merge topic 'vim-syntax'

ce540aea cmake-syntax.vim: Update the command list
Merge topic 'InstallRequiredSystemLibraries-vs-openmp'

d538c55e Help: Add notes for topic 'InstallRequiredSystemLibraries-vs-openmp'
bdb5007b InstallRequiredSystemLibraries: Install OpenMP runtime libs (#15117)
Merge topic 'bash-complete-ctest-labels'

2603e128 bash-completion: Complete 'ctest' label names
Merge topic 'xcode-assetcatalog-folder-type'

8eacc339 Xcode: Reference '.xcassets' folders as assetcatalog (#15125)
02aa5965 Xcode: Refactor internal file type extension extraction
Merge topic 'xcode-duplicate-file-refs'

d73f8828 Merge branch 'backport-xcode-duplicate-file-refs' into xcode-duplicate-file-refs
cf92fe2d Xcode: Generate per-target file references (#15111)
e7114226 Xcode: Generate per-target file references (#15111)
Merge topic 'doc-try_compile-debug-advice'

abbe91c5 Help: Clarify --debug-trycompile usage with try_compile
Merge topic 'doc-add_custom_command-multiple-commands'

412926d0 Help: Clarify add_custom_command multiple command behavior (#15112)
Merge branch 'master' into next
Merge branch 'release'
Merge branch 'master' into next