[clang] [Clang][Darwin] Centralize framework search paths for headers & libraries. (PR #118543)

[Cyndy Ishida via cfe-commits]

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@@ -339,13 +340,11 @@ void InitHeaderSearch::AddDefaultIncludePaths(
   if (triple.isOSDarwin()) {
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cyndyishida wrote:

I looked into this a bit more. IMO the only way to move all this code to the driver is to either 
 
1. changing search path order between Framework search paths & other default search paths like `-internal-isystem $(SDKROOT)/usr/include` (since existing `iframework` puts the search path at the top instead of at the bottom like what `InitHeaderSearch` does)
OR 
2. introducing some kind of search path argument to preserve back precedence for S/L/F e.g. a  `-internal-iframework`

Both feel out of scope to me. 

https://github.com/llvm/llvm-project/pull/118543