biology/htslib: fix build on armv7

This project includes some SIMD-enhanced functions for ARM NEON.
Unfortunately the code uses a bunch of intrinsics only available on
aarch64. Disable the use of NEON on armv6 and armv7 to fix the build
on these platforms.

See also: https://github.com/samtools/htslib/issues/1603
Approved by: portmgr (build fix blanket)