Merge tq's regex backend fixes (branch 'master' of https://github.com/thequux/hammer)

Makefile

common.mk

src/Makefile

src/backends/regex.c

src/backends/regex_debug.c

src/parsers/bits.c

src/parsers/ch.c

src/parsers/charset.c

src/parsers/ignoreseq.c

src/parsers/token.c

src/parsers/whitespace.c

src/system_allocator.c