ARM: Log an error if /proc/cpuinfo cannot be opened

This will make it easier to see if the current CPU feature detection
starts breaking because of process sandboxing.

BUG=v8:2597

Review URL: https://chromiumcodereview.appspot.com/13465003
Patch from Hans Wennborg <hans@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14112 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-linux.cc

@@ -111,8 +111,10 @@ static bool CPUInfoContainsString(const char * search_string) {
   FILE* f = NULL;
   const char* what = search_string;
 
-  if (NULL == (f = fopen(file_name, "r")))
+  if (NULL == (f = fopen(file_name, "r"))) {
+    OS::PrintError("Failed to open /proc/cpuinfo\n");
     return false;
+  }
 
   int k;
   while (EOF != (k = fgetc(f))) {