dev-perl/Bio-DB-HTS: allow explicit specification of htslib directories

dev-perl/Bio-DB-HTS: allow explicit specification of htslib directories

Upstream build script takes a single directory as htslib prefix, then
appends "include/htslib" while looking for header files and "lib" while
looking for library. Unsurprisingly, the latter fails to locate the htslib
library on SYMLINK_LIB=no systems.

I have patched the build script to allow both htslib-includedir and
htslib-libdir to be provided explicitly, thus letting the ebuild take
care of choosing the correct libdir name for the specified
architecture/ABI.

Closes: https://bugs.gentoo.org/654460
Package-Manager: Portage-2.3.24, Repoman-2.3.6