package/chrony: add optional support for libcap

When libcap was compiled before, chrony will use it as optional
dependency:

$ output/host/usr/bin/x86_64-linux-readelf -a output/target/usr/sbin/chronyd | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libcap.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.1]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/chrony/chrony.mk

@@ -16,6 +16,12 @@ CHRONY_CONF_OPTS = \
 	--without-seccomp \
 	--without-tomcrypt
 
+ifeq ($(BR2_PACKAGE_LIBCAP),y)
+CHRONY_DEPENDENCIES += libcap
+else
+CHRONY_CONF_OPTS += --without-libcap
+endif
+
 ifeq ($(BR2_PACKAGE_LIBNSS),y)
 CHRONY_DEPENDENCIES += host-pkgconf libnss
 else