Move calls of MaybeParseMicrosoftAttributes() before ParseExternalDeclaration()

into ParseDeclOrFunctionDefInternal() (which is called by
MaybeParseMicrosoftAttributes()), so that the attributes can be stored in
the DeclSpec.  No behavior change yet, part of https://reviews.llvm.org/D23895


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@280574 91177308-0d34-0410-b5e6-96231b3b80d8