Got test1-3 working on x86-64.

There are probably still issues on x86-64 I've missed.
I've added a few new tests to abitest, which fail (2x long long and 2x double
in a struct should be passed in registers).

tcc.h

@@ -1201,6 +1201,9 @@ ST_FUNC void decl(int l);
 #if defined CONFIG_TCC_BCHECK || defined TCC_TARGET_C67
 ST_FUNC Sym *get_sym_ref(CType *type, Section *sec, unsigned long offset, unsigned long size);
 #endif
+#ifdef TCC_TARGET_X86_64
+ST_FUNC int classify_x86_64_va_arg(CType *ty);
+#endif
 
 /* ------------ tccelf.c ------------ */