Adapt new runnable/test21241.d for LDC

Author: kinke

tests/dmd/fail_compilation/test21241.d

@@ -0,0 +1,23 @@
+/*
+REQUIRED_ARGS: runnable/imports/imp21241a.c runnable/imports/imp21241b.c
+*/
+// https://github.com/dlang/dmd/issues/21241
+
+/* LDC: no 'fix' for LDC (moved from runnable/ to fail_compilation/); make sure a warning is emitted instead
+        see https://github.com/ldc-developers/ldc/pull/4949#issuecomment-2972894481
+REQUIRED_ARGS: -w
+TEST_OUTPUT:
+---
+runnable/imports/imp21241a.c(3): Warning: skipping definition of function `imp21241a.foo` due to previous definition for the same mangled name: foo
+---
+*/
+
+import imp21241a;
+import imp21241b;
+
+void main(){
+    int x = getA();
+    assert(x==aValue);
+    x = getB();
+    assert(x==bValue);
+}