a ridiculous amount of propagation through the backend later,

have the code generate slap a srcloc metadata on inline asm nodes.
This allows us to diagnose invalid inline asms with such nice 
diagnostics as:

<inline asm>:1:2: error: unrecognized instruction
        abc incl    %eax
        ^
asm.c:2:12: note: generated from here
  __asm__ ("abc incl    %0" : "+r" (X));
           ^
2 diagnostics generated.

llvm-svn: 100608