tccgen: nocode_wanted alternatively

tccgen.c: remove any 'nocode_wanted' checks, except in
- greloca(), disables output elf symbols and relocs
- get_reg(), will return just the first suitable reg)
- save_regs(), will do nothing

Some minor adjustments were made where nocode_wanted is set.

xxx-gen.c: disable code output directly where it happens
in functions:
- g(), output disabled
- gjmp(), will do nothing
- gtst(), dto.

tccasm.c

@@ -915,8 +915,12 @@ static void asm_parse_directive(TCCState *s1)
 /* assemble a file */
 static int tcc_assemble_internal(TCCState *s1, int do_preprocess)
 {
+    int saved_nocode_wanted;
     int opcode;
 
+    saved_nocode_wanted = nocode_wanted;
+    nocode_wanted = 0;
+
     /* XXX: undefine C labels */
 
     ch = file->buf_ptr[0];
@@ -960,7 +964,7 @@ static int tcc_assemble_internal(TCCState *s1, int do_preprocess)
                 /* handle "extern void vide(void); __asm__("vide: ret");" as
                 "__asm__("globl vide\nvide: ret");" */
                 Sym *sym = sym_find(opcode);
-                if (sym && (sym->type.t & VT_EXTERN) && nocode_wanted) {
+                if (sym && (sym->type.t & VT_EXTERN) && saved_nocode_wanted) {
                     sym = label_find(opcode);
                     if (!sym) {
                         sym = label_push(&s1->asm_labels, opcode, 0);
@@ -989,6 +993,7 @@ static int tcc_assemble_internal(TCCState *s1, int do_preprocess)
 
     asm_free_labels(s1);
 
+    nocode_wanted = saved_nocode_wanted;
     return 0;
 }