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>

Makefile

@@ -484,6 +484,11 @@ all::
 #        The DEVELOPER mode enables -Wextra with a few exceptions. By
 #        setting this flag the exceptions are removed, and all of
 #        -Wextra is used.
+#
+#    pedantic:
+#
+#        Enable -pedantic compilation. This also disables
+#        USE_PARENS_AROUND_GETTEXT_N to produce only relevant warnings.
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN

config.mak.dev

@@ -1,6 +1,11 @@
 ifeq ($(filter no-error,$(DEVOPTS)),)
 CFLAGS += -Werror
 endif
+ifneq ($(filter pedantic,$(DEVOPTS)),)
+CFLAGS += -pedantic
+# don't warn for each N_ use
+CFLAGS += -DUSE_PARENS_AROUND_GETTEXT_N=0
+endif
 CFLAGS += -Wdeclaration-after-statement
 CFLAGS += -Wno-format-zero-length
 CFLAGS += -Wold-style-definition