Change the output of llvm-nm and llvm-size for Mach-O universal files (aka

fat files) to print “ (for architecture XYZ)” for fat files with more than
one architecture to be like what the darwin tools do for fat files.

Also clean up the Mach-O printing of archive membernames in llvm-nm to use
the darwin form of "libx.a(foo.o)".

llvm-svn: 211316