Rejigger Linux platform detection
This change makes some very small improvements to the Linux platform
detection logic. In particular, the existing logic did not work on my
Archlinux machine since /lib64/ld-linux-x86-64.so.2 isn't a symlink. In
that case, the detection logic should have fallen back to the slower
`ldd --version` technique, but `read_link` fails outright when its
argument isn't a symbolic link. So we tweak the logic to allow it to
fail, and if it does, we still try the `ldd --version` approach instead
of giving up completely.
I also made some cosmetic improvements to the regex matching, as well as
ensuring that the regexes are only compiled exactly once.
Andrew Gallant
294955ecff