[PATCH] D27545: Don't assert when redefining a built-in macro in a PCH, PR29119

[Nico Weber via Phabricator via cfe-commits]

thakis added a comment.

(The reason that the predefines buffer doesn't override the value of `__STDC_HOSTED__` from the pch is that CompilerInstance::createPCHExternalASTSource overrides the predefines buffer with a different predefines buffer suggested by the ASTReader, usually an empty one.)


https://reviews.llvm.org/D27545