[clang] clang: normalise inputs for Windows more aggresively (PR #181306)

[Saleem Abdulrasool via cfe-commits]

================
@@ -38,6 +38,28 @@ using namespace clang;
 
 #define DEBUG_TYPE "file-search"
 
+namespace {
+void NormalizeCacheKey(StringRef &Path, std::optional<std::string> &Storage) {
----------------
compnerd wrote:

I wonder if that has changed, we tended to aggressively use anonymous namespaces.

https://github.com/llvm/llvm-project/pull/181306