DOC: install: recommend pcre2

Makefile comments are also updated to recommend the PCRE2 related
options. PCRE1 is EOL by now:

   https://www.mail-archive.com/haproxy@formilux.org/msg41326.html

(cherry picked from commit 2192dfa6b69f499443afd0f4ffb74eea550d0ecb)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 5916f14d063cfa8fb2f910fb13b8aa069efc5c84)
[wt: trivial ctx adj]
Signed-off-by: Willy Tarreau <w@1wt.eu>
2 files changed