fetchmail: gettext is not mandatory

Even when locales are enabled, gettext is not mandatory to build
fetchmail, i.e the following defconfig builds fine:

BR2_arm=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_TOOLCHAIN_EXTERNAL_CUSTOM=y
BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD=y
BR2_TOOLCHAIN_EXTERNAL_URL="http://autobuild.buildroot.org/toolchains/tarballs/br-arm-full-2017.02-1096-g54a5333.tar.bz2"
BR2_TOOLCHAIN_EXTERNAL_GCC_4_8=y
BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_10=y
BR2_TOOLCHAIN_EXTERNAL_LOCALE=y
BR2_TOOLCHAIN_EXTERNAL_CXX=y
BR2_INIT_NONE=y
BR2_SYSTEM_BIN_SH_NONE=y
BR2_PACKAGE_FETCHMAIL=y

However, if gettext provides libintl, it gets used. Therefore this
commit moves gettext from a mandatory dependency to an optional
dependency.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/fetchmail/Config.in

@@ -4,7 +4,6 @@ config BR2_PACKAGE_FETCHMAIL
 	select BR2_PACKAGE_CA_CERTIFICATES
 	select BR2_PACKAGE_OPENSSL
 	select BR2_PACKAGE_ZLIB
-	select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT_IF_LOCALE
 	help
 	  Fetchmail - the mail-retrieval daemon
 	  Client daemon to move mail from POP and IMAP to your local computer

package/fetchmail/fetchmail.mk

@@ -20,8 +20,12 @@ FETCHMAIL_CONF_OPTS = \
 
 FETCHMAIL_DEPENDENCIES = \
 	ca-certificates \
-	openssl \
-	$(if $(BR2_NEEDS_GETTEXT_IF_LOCALE),gettext)
+	openssl
+
+# libintl is an optional dependency
+ifeq ($(BR2_PACKAGE_GETTEXT),y)
+FETCHMAIL_DEPENDENCIES += gettext
+endif
 
 # fetchmailconf.py script is not (yet) python3-compliant.
 # Prevent the pyc-compilation with python-3 from failing by removing this