test-lib: add LIBPCRE1 & LIBPCRE2 prerequisites

test-lib: add LIBPCRE1 & LIBPCRE2 prerequisites

Add LIBPCRE1 and LIBPCRE2 prerequisites which are true when git is
compiled with USE_LIBPCRE1=YesPlease or USE_LIBPCRE2=YesPlease,
respectively.

The syntax of PCRE1 and PCRE2 isn't the same in all cases (see
pcresyntax(3) and pcre2syntax(3)). If test are added that test for
those they'll need to be guarded by these new prerequisites.

The subsequent patch will make use of LIBPCRE2, so LIBPCRE1 isn't
strictly needed for now, but let's add it for consistency and so that
checking for it doesn't have to be done with the less obvious "PCRE,
!LIBPCRE2", which while semantically the same is more confusing, and
would lead to bugs if PCRE v3 is ever released as the tests would mean
v1, not any non-v2 version.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>