Add a warning when the llvm-nm -print-size flag is used on a Mach-O file as

Mach-O files don’t have size information about the symbols in the object file
format unlike ELF.

Also add the part of the fix to llvm-nm that was missed with r290001 so
-arch armv7m works.

rdar://25681018

llvm-svn: 293099