Fix sub-int returns on x86-64 and i386

the ABIs (and other compilers) extend sub-int return values in the
caller.  TCC extends them in the callee.  For compatibility with
those other compilers we have extend them in the caller as well.
That introduces a useless double extension in pure TCC-compiled code,
but fixing that generally requires that the code generator of TCC would
understand sub-int types.  For the time being bite the bullet.

i386-gen.c

@@ -369,6 +369,7 @@ static void gcall_or_jmp(int is_jmp)
         rt = vtop->type.ref->type.t;
         switch (rt & VT_BTYPE) {
             case VT_BYTE:
+            case VT_BOOL:
                 if (rt & VT_UNSIGNED) {
                     o(0xc0b60f); /* movzx %al, %eax */
                 }