Never use .lcomm on platforms where it does not accept an alignment

Never use .lcomm on platforms where it does not accept an alignment
argument.  Instead, use a pair of .local and .comm directives.

This avoids spurious differences between binaries built by the
integrated assembler vs. those built by the external assembler,
since the external assembler may impose alignment requirements
on .lcomm symbols where the integrated assembler does not.

llvm-svn: 168704