MC: make ELF .type handling more GNU AS compatible

GAS documents the .type directive as having an optional comma following the key
symbol name when using the STT_<TYPE_IN_UPPER_CASE> form.  However, it treats
the comma as optional in all cases.  This makes the IAS support both forms of
inputs.  Furthermore, the prefixed forms take either the upper case name or the
lower case alias.

The tests are split into two separate sets as the hash character serves as a
comment character on x86, which is tested in the second set by using arm-elf
which uses the at symbol as a comment character.

llvm-svn: 210407