--- spark-gpl-2017-src/gnat2why/gnat2why_c.gpr.old	2017-10-04 21:41:41.613376056 +0200
+++ spark-gpl-2017-src/gnat2why/gnat2why_c.gpr	2017-10-04 21:42:30.582572536 +0200
@@ -1,4 +1,7 @@
 project Gnat2Why_C is
    for Languages use ("C");
    for Object_Dir use "obj";
+   package Compiler is
+      for Driver ("C") use External ("CC", "gcc");
+   end Compiler;
 end Gnat2Why_C;