Turn off optimizations for all gcc versions in hash unit tests

Optimizations were turned off for g++ 4.8 to work around compiler bug
resulting in generating infinite loops for the code in this function in
052e598d09, but apparently other versions of g++
suffer from it as well, so just always turn them off until we can be sure
about the version of the compiler in which this bug was really fixed.

tests/hashes/hashes.cpp

@@ -382,9 +382,7 @@ void
 // code in this function and make all the loops below infinite when using -O2,
 // so we need to turn off optimizations for it to allow the tests to run at
 // all.
-#if __GNUC__ == 4 && __GNUC_MINOR__ == 8 && __GNUC_PATCHLEVEL__ < 3
 __attribute__((optimize("O0")))
-#endif // g++ 4.8.[012]
 #endif // g++
 HashMapTest()
 {