package/git: fix build with NLS enabled

package/git: fix build with NLS enabled

git fails to build with NLS enabled because of weak check
for gettext in configure.ac. The AC_CHECK_LIB(c, gettext ...)
is used to set LIBC_CONTAINS_LIBINTL variable. If the variable
is set then '-libs' is not passed to the linker, but this variable
is set to 'Yes' even libc implementation does not provide libintl
support, the AC_CHECK passes because gcc has gettext builtin.

So use instead AC_LINK_IFELSE with included libintl.h because it
makes gettext to unfold as libintl_gettext which causes AC_CHECK
to fail for cases when gettext is not provided by libc.

Tested by ./utils/test-pkg with NLS disabled/enabled.

Fixes:
	http://autobuild.buildroot.net/results/091b790ca6f5b46d5d29211dc1cb3ff05b62a965
	http://autobuild.buildroot.net/results/a69b58b35b270fdd2df9b076e7030bb594520197
	http://autobuild.buildroot.net/results/f104c4e6ff41b1dd175f2d27f3b4ea7c9b61f7c5
	http://autobuild.buildroot.net/results/ee12bdba398a139995de5f6f6718be6a493541d9
	http://autobuild.buildroot.net/results/74fa6b2bfbb1301e35c9dd1bbc04856c1cbf25f2

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>