Two more Windows-related fixes:

- More enum signeness bitfield fixes (MSVC treats enums as signed).

- Fixed in Lex/HeaderSearch.cpp an unsafe copy between two
  HeaderSearch::PerFileInfo entries in a common vector. The copy involved two
  calls to getFileInfo() within the assignment; these calls could have
  side-effects that enlarged the internal vector, and with MSVC this would
  invalidate one of the values in the assignment.
  
Patch by Argiris Kirtzidis!

llvm-svn: 47536