package/sane-airscan: propagate dependencies of selects

When the sane-airscan package was introduced in
f78280bf262ceb1c1abbdade9de77fcc4add74ae, the depends on of options
that is selects were not properly accounted for, so let's fix this.

Fixes:

WARNING: unmet direct dependencies detected for BR2_PACKAGE_GNUTLS
  Depends on [n]: !BR2_STATIC_LIBS [=n] && BR2_USE_WCHAR [=n]
  Selected by [y]:
  - BR2_PACKAGE_SANE_AIRSCAN [=y]

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/sane-airscan/Config.in

@@ -1,5 +1,9 @@
 config BR2_PACKAGE_SANE_AIRSCAN
 	bool "sane-airscan"
+	depends on !BR2_STATIC_LIBS # avahi, gnutls, sane-backends
+	depends on BR2_TOOLCHAIN_HAS_THREADS # avahi, dbus
+	depends on BR2_USE_WCHAR # avahi, gnutls
+	depends on BR2_USE_MMU # dbus, sane-backends
 	select BR2_PACKAGE_AVAHI
 	select BR2_PACKAGE_AVAHI_DAEMON # needed to get avahi-client
 	select BR2_PACKAGE_DBUS # needed by avahi to get avahi-client
@@ -18,3 +22,8 @@ config BR2_PACKAGE_SANE_AIRSCAN
 	  support "driverless" scanning.
 
 	  https://github.com/alexpevzner/sane-airscan
+
+comment "sane-airscan needs a toolchain w/ wchar, dynamic library, threads"
+	depends on BR2_USE_MMU
+	depends on !BR2_USE_WCHAR || BR2_STATIC_LIBS || \
+		!BR2_TOOLCHAIN_HAS_THREADS