Fix .dwsect generation for XCOFF. Handle .function generated with DWARF on XCOFF.
gas * config/tc-ppc.c (ppc_function): Update comment for
fifth argument.
(ppc_frob_symbol): Remove ppc_last_function check.
Make sure coff_last_function is reset.
Correctly set fsize when not provided in .function.
* testsuite/gas/ppc/aix.exp: New tests.
* testsuite/gas/ppc/xcoff-function-1-32.d: New test.
* testsuite/gas/ppc/xcoff-function-1-64.d: New test.
* testsuite/gas/ppc/xcoff-function-1.s: New test.