Use hardcoded path to gn binary

Index: src/util/exe_path.cc
--- src/util/exe_path.cc.orig
+++ src/util/exe_path.cc
@@ -117,13 +117,7 @@ base::FilePath GetExePath() {
 #else
 
 base::FilePath GetExePath() {
-  base::FilePath result;
-  const char kProcSelfExe[] = "/proc/self/exe";
-  if (!ReadSymbolicLink(base::FilePath(kProcSelfExe), &result)) {
-    NOTREACHED() << "Unable to resolve " << kProcSelfExe << ".";
-    return base::FilePath();
-  }
-  return result;
+  return base::FilePath("${LOCALBASE}/bin/gn");
 }
 
 #endif