package/transmission: fix gtk dependencies

Buildroot commit 80793107a65d95f8dfd0317a726d3a737c78ef67 forgot to add
packages needed for gtk support:
https://github.com/transmission/transmission/blob/main/CMakeLists.txt#L40

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
[yann.morin.1998@free.fr:
  - don't add dependencies to C++ or wh-char, already global deps
  - propagate sync-4 dependency to comment
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
diff --git a/package/transmission/Config.in b/package/transmission/Config.in
index fd4c897..eeaa789 100644
--- a/package/transmission/Config.in
+++ b/package/transmission/Config.in
@@ -37,11 +37,16 @@
 
 config BR2_PACKAGE_TRANSMISSION_GTK
 	bool "transmission-gtk"
+	depends on !BR2_nios2 # gtkmm3
+	depends on BR2_TOOLCHAIN_HAS_SYNC_4 # pangomm, libgtk3 -> pango -> harfbuzz -> gtkmm3
 	depends on BR2_PACKAGE_LIBGTK3 && BR2_SYSTEM_ENABLE_NLS
+	select BR2_PACKAGE_GTKMM3
 	help
 	  Install transmission GTK-based GUI interface.
 
-comment "transmission-gtk needs NLS enabled"
+comment "transmission-gtk needs libgtk3 and a toolchain with NLS enabled"
+	depends on !BR2_nios2
+	depends on BR2_TOOLCHAIN_HAS_SYNC_4
 	depends on BR2_PACKAGE_LIBGTK3 && !BR2_SYSTEM_ENABLE_NLS
 endif
 
diff --git a/package/transmission/transmission.mk b/package/transmission/transmission.mk
index f3a200c..26deeef 100644
--- a/package/transmission/transmission.mk
+++ b/package/transmission/transmission.mk
@@ -74,7 +74,7 @@
 
 ifeq ($(BR2_PACKAGE_TRANSMISSION_GTK),y)
 TRANSMISSION_CONF_OPTS += -DENABLE_GTK=ON
-TRANSMISSION_DEPENDENCIES += libgtk3
+TRANSMISSION_DEPENDENCIES += gtkmm3 libgtk3
 else
 TRANSMISSION_CONF_OPTS += -DENABLE_GTK=OFF
 endif