As it turns out I don't have modules which access /usr/local/lib without -L. I was presuming "whereis" would give both locations if there were multiple installs but it does not, it just reports the /usr/local one. However, there are distro versions of those libraries in /usr/lib64 (just not libmpg123). This is good, since that was kind of the most baffling part. WRT BUILD_NOISY, all it says about this is:

Starting Build Compile Stage
  Starting "perl Makefile.PL" Stage
Warning (mostly harmless): No library found for -lmpg123
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So I ran it through `strace -f` (the dirt is in a child, so just `strace` won't get it). Without `-L`, it stats in order /usr/local/lib64, /lib64, and then /usr/lib64. It's of course my laziness that /usr/local does not follow the convention of dividing 64 and 32 bit libs (since there aren't any of the later).

However, I still don't see why it doesn't use the actual compile time linker path. In the end, the use of `-L /usr/local/lib` is meaningless; it would have been found anyway if `-lmpg123` was used. But it seems if the afforementioned search failed, Inline leaves the "LIBS" command out entirely of its own accord. I'm on the mailing list so I'll ask about this...