Merging r367039 and r367103:

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r367039 | erichkeane | 2019-07-25 19:14:45 +0200 (Thu, 25 Jul 2019) | 6 lines

Remove CallingConvMethodType

This seems to be an old vestage of a previous implementation of getting
the default calling convention, and everything is now using
CXXABI/ASTContext's getDefaultCallingConvention.  Remove it, since it
isn't doing anything.
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r367103 | erichkeane | 2019-07-26 14:36:12 +0200 (Fri, 26 Jul 2019) | 6 lines

Make the CXXABIs respect the target's default calling convention.

SPIR targets need to have all functions be SPIR calling convention,
however the CXXABIs were just returning CC_C in all non-'this-CC' cases.

https://reviews.llvm.org/D65294
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llvm-svn: 367129