2. Added partial debug support for mingw\cygwin targets (the same as
   Linux\ELF). Please note, that currently mingw\cygwin uses 'stabs' format
   for storing debug info by default, thus many (runtime) libraries has
   this information included. These formats shouldn't be mixed in one binary
   ('stabs' & 'DWARF'), otherwise binutils tools will be confused.

llvm-svn: 31311

generated object modules to be debugged with gdb. Hopefully this helps
pre-release debugging.

llvm-svn: 31299

llvm-svn: 31203

llvm-svn: 30737

int x __attribute__((used));

to:

        .data
.comm _x,4              ; 'x'
        .no_dead_strip  _x

on both x86 and ppc darwin targets.

llvm-svn: 30605

llvm-svn: 30177

llvm-svn: 30161