Bad assumption make bad things happen:
long d3;
asm(..."1:\tdec %3\n\t" : ... "=&c" (d3)
Which wants 'dec RDI' but did 'dec EDI' on _WIN64.
Also:
- tcctest.c: enable more asm tests for win64
- configure: show errors if any with 'gcc conftest.c'
- tccgen.c: remove decl0(x, y, z)