PS2: Fix compilation with latest PS2SDK

[ccawley2011]

This compiles, but has not been tested.

[digitall]

Have reviewed. The code changes are limited to the PS2 port and are mostly fairly self-explanatory and unlikely to cause any regressions or build failures with the current toolchain on the buildbot.

The changes to the configure basically disable using the -pedantic GCC option (presumably as some GCC extensions are used in the system headers in newer SDK?), make some minor changes to allow Tremor to be disabled (even on older SDK where it was forced) and add the ijspcm library detection.

None of this should be an issue for older code or build toolchains, so am going to merge this as-is and the PS2 porter / power users (ie. self compiled builds) or users with buildbot builds can provide feedback if the builds start having any runtime issues. This is better than having this suffer bitrot as a PR.