Build breaks on 32-bit FreeBSD

[anevilyak]

On FreeBSD/i386, the build gets 99% of the way, but fails on the bash build step. Specifically, MkSigNamesExt1 fails, for the following reason:

In support/mksignames.c, the size of the signals array is defined by looking up the value of NSIG. Given the arithmetic, this yields an array of 64 entries. However, it also checks for SIGRTMIN AND SIGRTMAX. On FreeBSD these resolve to 65 and 126. As a consequence, it tries to also populate those entries, but these are out of the array's bounds and so it crashes. This can be fixed by using a similar workaround to what is done for AIX, where RTMIN and RTMAX are undef'd.

[bonefish]

I avoided touching the mksignames source. It wasn't correct to use it for cross-compilation anyway. The problem should be gone in r22092.