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.

tccasm.c

@@ -977,7 +977,8 @@ static void subst_asm_operands(ASMOperand *operands, int nb_operands,
             }
             modifier = 0;
             if (*str == 'c' || *str == 'n' ||
-                *str == 'b' || *str == 'w' || *str == 'h')
+                *str == 'b' || *str == 'w' ||
+                *str == 'h' || *str == 'k')
                 modifier = *str++;
             index = find_constraint(operands, nb_operands, str, &str);
             if (index < 0)
@@ -1029,7 +1030,8 @@ static void parse_asm_operands(ASMOperand *operands, int *nb_operands_ptr,
             skip('(');
             gexpr();
             if (is_output) {
-                test_lvalue();
+                if (!(vtop->type.t & VT_ARRAY))
+                    test_lvalue();
             } else {
                 /* we want to avoid LLOCAL case, except when the 'm'
                    constraint is used. Note that it may come from