Disable imake autodetection for:
- LinuxDistribution to avoid injection of /usr paths
- gcc to avoid use uf /usr/bin/gcc

https://github.com/NixOS/nixpkgs/issues/135337
--- a/imake.c
+++ b/imake.c
@@ -1065,6 +1065,7 @@ get_distrib(FILE *inFile)
   fprintf (inFile, "%s\n", "#define LinuxWare       11");
   fprintf (inFile, "%s\n", "#define LinuxYggdrasil  12");
 
+#if 0 /* disable system autodetection. Fall through to LinuxUnknown. */
 # ifdef CROSSCOMPILE
   if (CrossCompiling) {
       fprintf (inFile, "%s\n",
@@ -1090,6 +1091,7 @@ get_distrib(FILE *inFile)
      * at the content of /etc/debian_version */
     return;
   }
+#endif
   /* what's the definitive way to tell what any particular distribution is? */
 
   fprintf (inFile, "%s\n", "#define DefaultLinuxDistribution LinuxUnknown");
@@ -1337,6 +1339,7 @@ get_gcc_version(FILE *inFile, char *name)
 static boolean
 get_gcc(char *cmd)
 {
+#if 0 /* disable gcc autodetection. Fall through to explicitly set. */
   struct stat sb;
     static const char* gcc_path[] = {
 #if defined(linux) || \
@@ -1385,6 +1388,9 @@ get_gcc(char *cmd)
 	}
       }
     return FALSE;
+#endif
+    strcpy (cmd, IMAKE_COMPILETIME_CPP);
+    return TRUE;
 }
 
 #ifdef CROSSCOMPILE