Makefile: add a DEVOPTS flag to get pedantic compilation
In the interest of code hygiene, make it easier to compile Git with the
flag -pedantic.
Pure pedantic compilation with GCC 7.3 results in one warning per use of
the translation macro `N_`:
warning: array initialized from parenthesized string constant [-Wpedantic]
Therefore also disable the parenthesising of i18n strings with
-DUSE_PARENS_AROUND_GETTEXT_N=0.
Signed-off-by: Beat Bolli <dev+git@drbeat.li>
Signed-off-by: Junio C Hamano <gitster@pobox.com>