Fixes the code to work with fuse_gtest.py.

src/gtest-all.cc

@@ -33,6 +33,12 @@
 //
 // Sometimes it's desirable to build Google Test by compiling a single file.
 // This file serves this purpose.
+
+// This line ensures that gtest.h can be compiled on its own, even
+// when it's fused.
+#include <gtest/gtest.h>
+
+// The following lines pull in the real gtest *.cc files.
 #include "src/gtest.cc"
 #include "src/gtest-death-test.cc"
 #include "src/gtest-filepath.cc"