[clang] [clang][DependencyScanning] Track modules that resolve from sysroot. (PR #130634)

[Ben Langmuir via cfe-commits]

================
@@ -739,6 +748,12 @@ ModuleDepCollectorPP::handleTopLevelModule(const Module *M) {
   MDC.ScanInstance.getASTReader()->visitInputFileInfos(
       *MF, /*IncludeSystem=*/true,
       [&](const serialization::InputFileInfo &IFI, bool IsSystem) {
+        if (MD.IsInSysroot) {
+          auto FullFilePath = ASTReader::ResolveImportedPath(
+              PathBuf, IFI.UnresolvedImportedFilename, MF->BaseDirectory);
+          MD.IsInSysroot = FullFilePath->starts_with(CurrSysroot);
----------------
benlangmuir wrote:

Minor nit: string prefix is not correct for paths, it also needs to check that the next character in `FullFilePath` is a separator.  I'm surprised I can't find an existing utility for this in Path.h, but maybe we should add one.

https://github.com/llvm/llvm-project/pull/130634