Merge branch 'ab/pcre2-grep'

"git grep" compiled with libpcre2 sometimes triggered a segfault,
which is being fixed.

* ab/pcre2-grep:
grep: fix segfault under -P + PCRE2 <=10.30 + (*NO_JIT)
test-lib: add LIBPCRE1 & LIBPCRE2 prerequisites

diff --cc grep.c
Simple merge

diff --cc t/t7810-grep.sh
Simple merge