[clang] [clang][deps] Load module map file from PCM (PR #66389)

[Ben Langmuir via cfe-commits]

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@@ -1307,6 +1307,9 @@ void ModuleMap::setInferredModuleAllowedBy(Module *M,
 
 std::error_code
 ModuleMap::canonicalizeModuleMapPath(SmallVectorImpl<char> &Path) {
+  FileManager &FM = SourceMgr.getFileManager();
+  FM.makeAbsolutePath(Path);
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benlangmuir wrote:

Is the idea that because the paths used by the scanner is now indirected through the (implicit) pcm that whatever ASTWriter does to make the path relative will apply to the explicit module invocation?  Before your current changes the scanner was using `canonicalizeModuleMapPath` directly on the path in the invocation, which is what I was naively thinking of.  

https://github.com/llvm/llvm-project/pull/66389