ci,cgen: fix windows tests

Author: spytheman

vlib/v/gen/c/cgen.v

@@ -744,7 +744,12 @@ pub fn gen(files []&ast.File, mut table ast.Table, pref_ &pref.Preferences) GenO
 	extern_out_str := g.extern_out.str()
 	b.write_string(out_str)
 	b.writeln('// THE END.')
-	b.write_string2('\n // V postincludes:\n', g.postincludes.str())
+
+	postincludes_str := g.postincludes.str()
+	if postincludes_str != '' {
+		b.write_string2('\n // V postincludes:\n', postincludes_str)
+	}
+
 	util.timing_measure('cgen common')
 	$if trace_all_generic_fn_keys ? {
 		gkeys := g.table.fn_generic_types.keys()

vlib/v/gen/c/testdata/postinclude_header.h

@@ -1,6 +1,10 @@
 #include <assert.h>
 
-int main( void ) {
+#if defined(_WIN32)
+int WINAPI wWinMain(HINSTANCE instance, HINSTANCE prev_instance, LPWSTR cmd_line, int show_cmd){
+#else
+int main(int argc, char *argv[]) {
+#endif    
    	int res = no_main__f(42);
 	assert(res == 987);
     return 0;