As we are compiling with -D_BSD_SOURCE, sigjmp_buf and siglongjmp
should be replaced by the non-sig functions (see man 3 setjmp).
Tested on linux/cell.
Fixes a segfault and better code. Unfortunately using an arbitrary
register ("=r") causes the gcc to abort when the code is optimized saying
it can't satisfy the constraint. Setting seems to do the trick.
I was waiting for the need to use this code to arise, and it finally came.
I've tested building this on Linux and Windows, both x86 and x64_64. But
it might break other platforms. Please bear with me and help me fix it.
Many thanks to Dennis Smit who submitted this, and Eric Anholt whose
work this was based on.
It still needs a slight code massasing to integrate with the rest of
gallium (namely mapping the OS_* ARCH_* defines), but I'm commiting anyway
so that it is available to be used when somebody needs it.
