Check for argument leagake over languages.

test cases/23 global arg/builder.txt

@@ -1,7 +1,7 @@
 project('global arg test', 'c++', 'c')
 
-add_global_arguments('c', '-Werror', '-DMYTHING')
+add_global_arguments('c', '-DMYTHING')
-add_global_arguments('c++', '-Werror', '-std=c++11')
+add_global_arguments('c++', '-DMYCXXTHING')
 
 exe1 = executable('prog', 'prog.c')
 exe2 = executable('prog2', 'prog.cc')

test cases/23 global arg/prog.c

@@ -2,6 +2,10 @@
 #error "Global argument not set"
 #endif
 
+#ifdef MYCXXTHING
+#error "Wrong global argument set"
+#endif
+
 int main(int argc, char **argv) {
     return 0;
 }

test cases/23 global arg/prog.cc

@@ -1,4 +1,10 @@
-#include<unordered_map>
+#ifdef MYTHING
+#error "Wrong global argument set"
+#endif
+
+#ifndef MYCXXTHING
+#error "Global argument not set"
+#endif
 
 int main(int argc, char **argv) {
     return 0;