package/mokutil: select libxcrypt if needed

Fix the following build failure raised since the addition of the package
in commit 2e6e121496:

mokutil.c:45:10: fatal error: crypt.h: No such file or directory
   45 | #include <crypt.h>
      |          ^~~~~~~~~

Fixes: 2e6e121496
 - http://autobuild.buildroot.org/results/59e470ad6bf7f48314cd26ed4163c095e4c803ab

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mokutil/Config.in

@@ -12,6 +12,7 @@ config BR2_PACKAGE_MOKUTIL
 	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_12 # efivar
 	select BR2_PACKAGE_EFIVAR
 	select BR2_PACKAGE_KEYUTILS
+	select BR2_PACKAGE_LIBXCRYPT if BR2_TOOLCHAIN_USES_GLIBC
 	select BR2_PACKAGE_OPENSSL
 	help
 	  mokutil is a tool to import or delete the machines owner

package/mokutil/mokutil.mk

@@ -14,6 +14,7 @@ MOKUTIL_DEPENDENCIES = \
 	efivar \
 	host-pkgconf \
 	keyutils \
+	$(if $(BR2_PACKAGE_LIBXCRYPT),libxcrypt) \
 	openssl
 
 $(eval $(autotools-package))