Ninja: Update showIncludes prefix detection for clang-cl 18
Since commit LLVM/Clang commit 5523fefb01c2
([clang][lex] Use
preferred path separator in includer-relative lookup, 2023-09-08), part
of the upcoming 18.x release, the output format of the showIncludes flag
has changed, where it now prints paths with double backslashes:
Note: including file: .\\foo.h
Previously, we expected to see the path name in the form "./foo.h".
Extend the regex to match a path name starting with .\
,
in addition to the existing matched patterns.
Backport: release
Topic-rename: clang-cl-showIncludes
Edited by Brad King