x11-toolkits/py-wxPython30: Unbreak on F10

It turns out that wxPython30 won't build with clang at all. The c++ code
is illegal according to clang (e.g. illegal cast), so remove the
USES=compiler setting and replace with USE_GCC=yes. Tested on F8 and F10.
I apologize for adding the GCC dependence for F10+ users but I didn't see
any other simple fix.

Approved by: blanket