fail style gate if C API builtins are missing

Author: lukasstadler

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiCodeGen.java

@@ -512,8 +512,7 @@ public static void main(String[] args) throws IOException {
         changed |= generateCApiSource(javaBuiltins);
         changed |= generateCApiHeader(javaBuiltins);
         changed |= generateBuiltinRegistry(javaBuiltins);
-
-        checkImports(allBuiltins);
+        changed |= checkImports(allBuiltins);
         if (changed) {
             System.exit(-1);
         }