[ms-inline asm] Have patchMSAsmStrings() return a vector or AsmStrings.

The AsmParser expects a single asm instruction, but valid ms-style inline asm
statements may contain  multiple instructions.

This happens with asm blocks

__asm {
  mov ebx, eax
  mov ecx, ebx
}

or when multiple asm statements are adjacent to one another

__asm mov ebx, eax
__asm mov ecx, ebx

and

__asm mov ebx, eax __asm mov ecx, ebx

Currently, asm blocks are not properly handled.

llvm-svn: 161780