[clang] Reland [clang-cl] Add new option /pathmap:<from>=<to> to replace the path prefix <from> with <to>. (PR #202830)

[via cfe-commits]

gulfemsavrun wrote:

The test added by this patch (`Preprocessor/cl-pathmap.c`) is failing on our Mac arm64 toolchain builders.
```
FAIL: Clang :: Preprocessor/cl-pathmap.c (19304 of 24822)
******************** TEST 'Clang :: Preprocessor/cl-pathmap.c' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 5
/Users/swarming/b/s/w/ir/x/w/llvm_build/bin/clang --driver-mode=cl --target=x86_64-windows-msvc -E /pathmap:/Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor=x:/path-to/ -- /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c | /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/FileCheck /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c --check-prefix CHECK-REPRODUCABLE
# executed command: /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/clang --driver-mode=cl --target=x86_64-windows-msvc -E /pathmap:/Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor=x:/path-to/ -- /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c
# executed command: /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/FileCheck /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c --check-prefix CHECK-REPRODUCABLE
# RUN: at line 10
/Users/swarming/b/s/w/ir/x/w/llvm_build/bin/clang --driver-mode=cl -E /pathmap:/Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor=. /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c | /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/FileCheck /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c --check-prefix CHECK-SIMPLE
# executed command: /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/clang --driver-mode=cl -E /pathmap:/Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor=. /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c
# .---command stderr------------
# | clang: warning: '/Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c' treated as the '/U' option [-Wslash-u-filename]
# | clang: note: use '--' to treat subsequent arguments as filenames
# | clang: error: no input files
# `-----------------------------
# error: command failed with exit status: 1
# executed command: /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/FileCheck /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c --check-prefix CHECK-SIMPLE
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /Users/swarming/b/s/w/ir/x/w/llvm_build/bin/FileCheck /Users/swarming/b/s/w/ir/x/w/llvm-llvm-project/clang/test/Preprocessor/cl-pathmap.c --check-prefix CHECK-SIMPLE
# `-----------------------------
# error: command failed with exit status: 2

--
```

https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-mac-arm64/b8679411821292782737/overview

https://github.com/llvm/llvm-project/pull/202830