configure: fix a regression in PCRE v1 detection

Change the check for PCRE v1 to disable the --with-libpcre1 option if the pcre_version() function can't be found in the pcre library. I unintentionally changed this in my 94da9193a6 ("grep: add support for PCRE v2", 2017-06-01) while renaming moving some variables. The intent of this check ever since it was added in a119f91e57 ("configure: Check for libpcre", 2011-05-09) is to second-guess the user and turn off an explicitly provided --with-libpcre if the library can't be found. I don't think that behavior makes any sense, we shouldn't be second-guessing the user with an auto-detection, but changing that needs a bigger refactoring of this script, and only has marginal benefits. So let's fix it to work as it was intended to work again. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>