Add gcc version check before add -fno-expensive-optimizations flag.
Only when gcc version is lower than 5.3.0, this flag is needed.
More bug info see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67736
https://gcc.gnu.org/ml/gcc-patches/2012-05/msg00401.htmlSigned-off-by: Shiyou Yin <yinshiyou-hf@loongson.cn>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>