libnds 1.5.6

[WinterMute]

libnds 1.5.6 is now available through the windows installer as usual and from the getting started page on the wiki.

libnds 1.5.6

• switch exit code to arm mode. Latest binutils won't insert interworking code for the calls to external asm here.
• fix to eeprom detection code when the spi bus returns 0s.
• Added memory barriers to videoGL.h to combat gcc 4.7.0 optimization.

The memory barrier code still needs reworked a bit for readability, I just wanted to get this fix out fairly quickly because all the 3D code is broken without it.