--- a/gnat2why/gnat2why_c.gpr	2017-10-04 21:41:41.613376056 +0200
+++ b/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;
--- a/gnatprove/configuration.adb	2019-11-08 19:20:16.876198539 +0100
+++ b/gnatprove/configuration.adb	2019-11-08 19:21:13.550201663 +0100
@@ -694,7 +694,9 @@
          Tree         : Project_Tree;
 
       begin
-         Set_Path_From_Gnatls (Proj_Env.all, "gnatls", GNAT_Version);
+         Set_Path_From_Gnatls (Proj_Env.all,
+                               "gnatls",
+                               GNAT_Version);
          Free (GNAT_Version);
          Set_Object_Subdir (Proj_Env.all, Subdir_Name);
          Proj_Env.Register_Default_Language_Extension ("C", ".h", ".c");