git: fix build with NLS disabled

git: fix build with NLS disabled

Since commit bbfb02598bf75 (git: use the new gettext logic) host-gettext is no
longer an unconditional dependency of git. When NLS is disabled host-gettext
is not built. This breaks the build of git, because the git Makefile runs
msgfmt unless NO_GETTEXT is defined.

Define NO_GETTEXT when NLS is disabled to fix the build.

Fixes:
http://autobuild.buildroot.net/results/c87/c8717619a1307f21cb9fe61196511cea44f72015/
http://autobuild.buildroot.net/results/e7a/e7acff51f988c333c3fe0c4a18eed42a273932d3/
http://autobuild.buildroot.net/results/153/153b17959847ec2079883c087cee27afbdf9571e/

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Sagaert Johan <sagaert.johan@skynet.be>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>