build: Fix boost build on some platforms

When the libpath doesn't line up with the value from config.sub, we don't find
the correct path to boost's libs. This adds a hack to try another path before
giving up.
build: fix FDELT_TYPE configure check

This probably never worked properly. Confirmed working now with every compiler
I throw at it.

Rebased-From: 8021cf8
Merge pull request #683 from rnicoll/1.8.1-dev-build2

Fix build autoconf rules for boost and fdelt_chk