"Fix" a problem with debug info in the presence of always_inline

function calls.  For a program like this:

#include <stdio.h>
static __inline__ __attribute__((always_inline)) 
int bar(int x) { return 4; }
int main() { 
  int X = bar(4);
  printf("%d\n", X);
}

clang was not outputing any debug info for the body of main().  This is
because the backend is getting confused by the region_start/end that clang
is emitting for block scopes.  For now, just disable these (matching llvm-gcc),
this stuff is in progress of rework anyway.

llvm-svn: 70889