firefox: add explicit dependency on gtk+3

* it used to be pulled into firefox's dependency tree by libnofity, but
  since:
  https://git.openembedded.org/openembedded-core/commit/?id=da15d7cf3e6f31c92232f8dd7272ea9ee41656db
  libnotify doesn't depend on gtk+3 by default

* with current oe-core/master it fails with:
 0:05.33 checking for nodejs... /OE/build/test-oe-build-time/poky/build/tmp/work/core2-64-poky-linux/firefox/68.9.0esr-r0/recipe-sysroot-native/usr/bin/node (14.17.1)
 0:05.33 checking for gtk+-wayland-3.0 >= 3.10 xkbcommon >= 0.4.1... no
 0:05.33 ERROR: Package gtk+-wayland-3.0 was not found in the pkg-config search path.
 0:05.33 ERROR: Perhaps you should add the directory containing `gtk+-wayland-3.0.pc'
 0:05.33 ERROR: to the PKG_CONFIG_PATH environment variable
 0:05.33 ERROR: No package 'gtk+-wayland-3.0' found
 0:05.33 ERROR: Package xkbcommon was not found in the pkg-config search path.
 0:05.33 ERROR: Perhaps you should add the directory containing `xkbcommon.pc'
 0:05.33 ERROR: to the PKG_CONFIG_PATH environment variable
 0:05.33 ERROR: No package 'xkbcommon' found
 0:05.37 *** Fix above errors and then restart with\
 0:05.37                "./mach build"
 0:05.37 make: *** [client.mk:115: configure] Error 1
WARNING: exit code 2 from a shell command.

Signed-off-by: Martin Jansa <[email protected]>

Author: shr-project

meta-firefox/recipes-browser/firefox/firefox_68.9.0esr.bb

@@ -7,6 +7,7 @@ DEPENDS += "curl startup-notification libevent cairo libnotify \
             nodejs-native cbindgen-native \
             yasm-native nasm-native unzip-native \
             virtual/${TARGET_PREFIX}rust cargo-native ${RUSTLIB_DEP} \
+            gtk+3 \
            "
 RDEPENDS:${PN}-dev = "dbus"