rbgdkdisplay.c:450:22: error: implicit declaration of function 'gdk_x11_display_get_startup_notification_id' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
4 warnings and 1 error generated.
make: *** [rbgdkdisplay.o] Error 1
In Gemfile:
gtk2
bundle config --local build.gtk2 "--with-cflags=-Wno-implicit-function-declaration"
で強行突破