grep: work around UTF-8 related JIT bug in PCRE2 <= 10.34

grep: work around UTF-8 related JIT bug in PCRE2 <= 10.34

Stephane is reporting[1] a regression introduced in git v2.40.0 that leads
to 'git grep' segfaulting in his CI pipeline. It turns out, he's using an
older version of libpcre2 that triggers a wild pointer dereference in
the generated JIT code that was fixed in PCRE2 10.35.

Instead of completely disabling the JIT compiler for the buggy version,
just mask out the Unicode property handling as we used to do prior to
commit acabd2048ee0 ("grep: correctly identify utf-8 characters with
\{b,w} in -P").

[1] https://lore.kernel.org/git/7E83DAA1-F9A9-4151-8D07-D80EA6D59EEA@clumio.com/

Reported-by: Stephane Odul <stephane@clumio.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>