Fix undefined symbols when loading the library
Fix undefined symbols when loading the library

$ make && ldd -r mgba_libretro.so
undefined symbol: powf  (./mgba_libretro.so)
undefined symbol: sqrt  (./mgba_libretro.so)
undefined symbol: sincosf       (./mgba_libretro.so)

$ make DEBUG=1 && ldd -r mgba_libretro.so
undefined symbol: sinf  (./mgba_libretro.so)
undefined symbol: powf  (./mgba_libretro.so)
undefined symbol: cosf  (./mgba_libretro.so)
undefined symbol: sqrt  (./mgba_libretro.so)

libretro/mgba,libretro/mgba,libretro/mgba,libretro/mgba,libretro/mgba