Update required version of GCC to 5.3.0 to enable Vc in ROOT
Update required version of GCC to 5.3.0 to enable Vc in ROOT

The static_assert() in Vc/common/simdize.h:758 is triggering due to
some strange interaction between the pragmas to suppress the warnings
and other things (see commit a79d073ef7). Newer versions of GCC seem
unaffected by this problem, so we require a recent enough GCC from
now on to sidestep this issue.

zzxuanyuan/root,zzxuanyuan/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,zzxuanyuan/root,zzxuanyuan/root,zzxuanyuan/root,karies/root,zzxuanyuan/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,karies/root,karies/root,olifre/root,root-mirror/root,zzxuanyuan/root,olifre/root,olifre/root,olifre/root,karies/root,karies/root,karies/root,karies/root,root-mirror/root,zzxuanyuan/root,root-mirror/root,karies/root,zzxuanyuan/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,zzxuanyuan/root,root-mirror/root,karies/root,root-mirror/root,karies/root,olifre/root,olifre/root,root-mirror/root