games/libretro-snes9x2010: fix build

• Fix build by changing gcc-specific argument to clang compatible (-flto=auto -> -flto). This change was upstreamed so it may be dropped on the next port update. For FreeBSD 11, don't use -flto at all to also fix the build.
• While here, minor style fixes

Approved by: portmgr blanket

(cherry picked from commit b842770973b7a381cf5f2b596a6bf7da04be418b)