[clang] [clang][Modules] Respect case sensitivity when hashing implicit module map path (PR #226339)

[Jan Svoboda via cfe-commits]

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@@ -59,19 +58,72 @@
 // CHECK-NEXT:         }
 // CHECK-NEXT:       ]
 
-//--- cdb.json.template
+// This overlay is used just to force the filesystem to be case sensitive to
+// simulate case insensitive access via diffierent capitalizations.
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jansvoboda11 wrote:

I think the important property here is that this VFS will return differently-capitalized results from `realpath` (respecting the capitalization you give it). That's in contrast with many real file systems, which will always return the canonical spelling. IUUC, this is critical for this test (and the newly-added one as well).

https://github.com/llvm/llvm-project/pull/226339