x86_64-asm: =m operand fixes

x86_64-asm: =m operand fixes

The problem was with tcctest.c:

    unsigned set;
    __asm__("btsl %1,%0" : "=m"(set) : "Ir"(20) : "cc");

when with tcc compiled with the HAVE_SELINUX option, run with
tcc -run, it would use large addresses far beyond the 32bits
range when tcc did not use the pc-relative mode for accessing
'set' in global data memory.  In fact the assembler did not
know about %rip at all.

Changes:
- memory operands use (%rax) not (%eax)
- conversion from VT_LLOCAL: use type VT_PTR
- support 'k' modifier
- support %rip register
- support X(%rip) pc-relative addresses

The test in tcctest.c is from Michael Matz.