package/qemu: add optional dependency on nettle

Qemu can optionally depend on nettle if available, so we should take
into account this optional dependency.

Cc: Florian Wolters <florian@florian-wolters.de>
Signed-off-by: Alexander Dahl <post@lespocky.de>
[Thomas: reword commit log, so that it makes sense in the context of
upstream Buildroot]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/qemu/qemu.mk

@@ -97,6 +97,13 @@ else
 QEMU_OPTS += --disable-libssh2
 endif
 
+ifeq ($(BR2_PACKAGE_NETTLE),y)
+QEMU_OPTS += --enable-nettle
+QEMU_DEPENDENCIES += nettle
+else
+QEMU_OPTS += --disable-nettle
+endif
+
 # Override CPP, as it expects to be able to call it like it'd
 # call the compiler.
 define QEMU_CONFIGURE_CMDS