Global inline assembler blocks are merged before parsing, so no specific

Global inline assembler blocks are merged before parsing, so no specific
location data is available. If pragma handling wants to look up the
position, it finds the LLVM buffer and wants to compare it with the
special built-in buffer, failing badly. Extend to the special handling
of the built-in buffer to also check for the inline asm buffer. Expect
only a single asm buffer. Sort it between the built-in buffers and the
normal file buffers.

Fixes the assert part of PR 22576.

llvm-svn: 232389