Without the change build fails on -fno-common toolchains like upstream
gcc-10 as:
$ nix build -L --impure --expr 'with import ./. {}; bwa.overrideAttrs (oa: { NIX_CFLAGS_COMPILE = (oa.NIX_CFLAGS_COMPILE or "") + "-fno-common"; })'
...
ld: ./libbwa.a(rope.o):/build/bwa-0.7.17/rle.h:33:
multiple definition of `rle_auxtab'; ./libbwa.a(bwtindex.o):/build/bwa-0.7.17/rle.h:33: first defined here
ld: ./libbwa.a(rle.o):/build/bwa-0.7.17/rle.h:33:
multiple definition of `rle_auxtab'; ./libbwa.a(bwtindex.o):/build/bwa-0.7.17/rle.h:33: first defined here