[MC] Sort FDEs by the associated CIE before emitting them.

This isn't necessary according to the DWARF standard, but it matches the
.eh_frame sections emitted by other tools in practice, and the Android
libunwindstack rejects .eh_frame sections where an FDE refers to a CIE
other than the closest previous CIE. So match the other tools and also
sort accordingly.

I consider this a bug in libunwindstack, but it's easy enough to emit
a compatible .eh_frame section for compatibility with installed
operating systems.

Differential Revision: https://reviews.llvm.org/D58266

llvm-svn: 356216