Make dump_syms 64-bit on Mac

Make dump_syms 64-bit on Mac.

The framework's grown to the point that 32-bit dump_syms no longer has enough
memory to do its job. It is failing with messages like:

dump_syms(12345) malloc: *** mmap(size=2097152) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug
dump_syms(12345) malloc: *** mmap(size=2097152) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug
dump_syms(12345) malloc: *** mmap(size=2097152) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug
terminate called after throwing an instance of 'St9bad_alloc'
  what():  std::bad_alloc

Moving to 64-bit gives it more space to work with. 64-bit dump_syms is able to
dump 32-bit files.

BUG=102361
TEST=Breakpad-enabled official release builds
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=107947

[Nico, 2011-10-31 14:06:14]

LGTM