Add more detailed warning if libfips binary could not be found.

Since we now may not compile a non-native bit-size libfips, (such as
not compiling libfips-32.so on a native 64-bit install), then fips can
fail when trying to wrap a 32-bit application.

So be kind and suggest that the user install gcc-multilib and
re-compile fips as one potential solution for this problem.