[clang] Introduce diagnostics suppression mappings (#112517)

This implements

https://discourse.llvm.org/t/rfc-add-support-for-controlling-diagnostics-severities-at-file-level-granularity-through-command-line/81292.

Users now can suppress warnings for certain headers by providing a
mapping with globs, a sample file looks like:
```
[unused]
src:*
src:*clang/*=emit
```

This will suppress warnings from `-Wunused` group in all files that
aren't under `clang/` directory. This mapping file can be passed to
clang via `--warning-suppression-mappings=foo.txt`.

At a high level, mapping file is stored in DiagnosticOptions and then
processed with rest of the warning flags when creating a
DiagnosticsEngine. This is a functor that uses SpecialCaseLists
underneath to match against globs coming from the mappings file.

This implies processing warning options now performs IO, relevant
interfaces are updated to take in a VFS, falling back to RealFileSystem
when one is not available.

1 files changed, 1 insertions, 1 deletions

diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
index cab5838..d1bac09 100644
--- a/clang/lib/Frontend/PrecompiledPreamble.cpp
+++ b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -479,7 +479,7 @@ llvm::ErrorOr<PrecompiledPreamble> PrecompiledPreamble::Build(
 
   // Clear out old caches and data.
   Diagnostics.Reset();
-  ProcessWarningOptions(Diagnostics, Clang->getDiagnosticOpts());
+  ProcessWarningOptions(Diagnostics, Clang->getDiagnosticOpts(), *VFS);
 
   VFS =
       createVFSFromCompilerInvocation(Clang->getInvocation(), Diagnostics, VFS);