Little hack to let you turn off searching for precompiled headers.
Really just here for benchmarking the effect on the preprocessor.
Signed-off-by: dank@kegel.com

diff -Nuar gcc-4.1-20060217/libcpp/files.c gcc-4.1-20060227/libcpp/files.c
--- gcc-4.1-20060217/libcpp/files.c	2005-11-03 18:10:19.000000000 -0800
+++ gcc-4.1-20060227/libcpp/files.c	2006-02-27 17:20:35.000000000 -0800
@@ -28,6 +28,7 @@
 #include "mkdeps.h"
 #include "hashtab.h"
 #include "md5.h"
+#include <stdlib.h>
 #include <dirent.h>
 
 /* Variable length record files on VMS will have a stat size that includes
@@ -248,9 +249,16 @@
   char *pchname;
   struct stat st;
   bool valid = false;
+  static int my_first_run = 1;
+  static int my_gcc_no_search_pch;
+
+  if (my_first_run) {
+    my_gcc_no_search_pch = (getenv("GCC_NO_SEARCH_PCH") != NULL);
+    my_first_run = 0;
+  }
 
   /* No PCH on <stdin> or if not requested.  */
-  if (file->name[0] == '\0' || !pfile->cb.valid_pch)
+  if (file->name[0] == '\0' || !pfile->cb.valid_pch || my_gcc_no_search_pch)
     return false;
 
   flen = strlen (path);