Improve error when trying to use an extern const as a compile time constant. #2969

test/test_suite/compile_time/extern_is_not_const.c3

@@ -0,0 +1,16 @@
+module test;
+import std;
+
+extern const void* FOO @cname("malloc");
+
+macro foo($x) {}
+
+fn void test()
+{
+	var $x = FOO; // #error: $x must be assigned a compile-time constant. 'extern' constants are resolved
+}
+
+fn void test2()
+{
+	foo(FOO); // #error: $x must be assigned a compile-time constant. 'extern' constants are resolved
+}