Correct PrivateLinkage for COFF

- Use storage class C_STAT for 'PrivateLinkage' The storage class for
  PrivateLinkage should equal to the Internal Linkage.

- Set 'PrivateGlobalPrefix' from "L" to ".L" for MM_WinCOFF (includes
  x86_64) MM_WinCOFF has empty GlobalPrefix '\0' so PrivateGlobalPrefix
  "L" may conflict to the normal symbol name starting with 'L'.

Based on a patch by Han Sangjin! Manually updated test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284096 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed