x86: Pass -O0 to assembler for some tests
* testsuite/gas/i386/att-regs.d: Pass -O0 to assembler.
* testsuite/gas/i386/avx512bw-intel.d: Likewise.
* testsuite/gas/i386/avx512bw.d: Likewise.
* testsuite/gas/i386/avx512f-intel.d: Likewise.
* testsuite/gas/i386/avx512f.d: Likewise.
* testsuite/gas/i386/disp32.d: Likewise.
* testsuite/gas/i386/intel-regs.d: Likewise.
* testsuite/gas/i386/pseudos.d: Likewise.
* testsuite/gas/i386/x86-64-disp32.d: Likewise.
* testsuite/gas/i386/x86-64-pseudos.d: Likewise.