Reapply r185872 now that the address sanitizer has been changed to support this.

Original commit message:

Stop emitting weak symbols into the "coal" sections.

The Mach-O linker has been able to support the weak-def bit on any symbol for
quite a while now. The compiler however continued to place these symbols into a
"coal" section, which required the linker to map them back to the base section
name.

Replace the sections like this:

  __TEXT/__textcoal_nt   instead use  __TEXT/__text
  __TEXT/__const_coal    instead use  __TEXT/__const
  __DATA/__datacoal_nt   instead use  __DATA/__data

<rdar://problem/14265330>

llvm-svn: 187939