Complete the existing support of ARM v6m, v7m, and v7em, i.e., respectively...

Complete the existing support of ARM v6m, v7m, and v7em, i.e., respectively cortex-m0, cortex-m3, and cortex-m4 on the backend side.

Adds new subtype values for the MachO format and use them when the related triple are set.

llvm-svn: 172472