Make dependency upon gtk optional

Signed-off-by: Alexander Golubev <fatzer2@gmail.com>

CMakeLists.txt

@@ -46,10 +46,14 @@ tde_setup_paths( )
 
 ##### optional stuff ############################
 
-option( WITH_BACKEND_LIBBFD "Build with libbfd backend" "ON" )
+option( WITH_BACKEND_LIBBFD   "Build with libbfd backend"    ON  )
-option( WITH_BACKEND_LIBELF "Build with libelf backend" "OFF" )
+option( WITH_BACKEND_LIBELF   "Build with libelf backend"    OFF )
-option( WITH_BACKEND_READONLY "Build with read-only backend" "OFF" )
+option( WITH_BACKEND_READONLY "Build with read-only backend" OFF )
+option( WITH_GTK              "Build support for GTK"        OFF )
 
+# NOTE: WITH_GTK build gtk bindings to ease libr in gtk applications.
+#       It uses weak linkage, so gtk will be required during build
+#       only and not strictly necessary during runtime.
 
 #### configure checks ###########################
 
@@ -95,10 +99,12 @@ if( NOT ZLIB_FOUND )
     tde_message_fatal( "zlib are required, but not found on your system" )
 endif( NOT ZLIB_FOUND )
 
+if( WITH_GTK )
     pkg_search_module( GTK gtk+-2.0 )
     if( NOT GTK_FOUND )
         tde_message_fatal( "gtk2 is required but was not found on your system" )
     endif( )
+endif( WITH_GTK )
 
 set( DL_LIBRARIES dl )
 check_library_exists( ${DL_LIBRARIES} dlopen /lib HAVE_LIBDL )

src/CMakeLists.txt

@@ -34,10 +34,13 @@ set( ${target}_SRCS
   onecanvas.c
   libr-icons.c
   libr-i18n.c
-  libr-gtk.c
   libr.c
 )
 
+if( WITH_GTK )
+    list( APPEND ${target}_SRCS libr-gtk.c )
+endif( WITH_GTK )
+
 tde_add_library(
   ${target} SHARED
   VERSION 1.0.0
@@ -61,10 +64,13 @@ set( ${target}_INCLUDES
   gettext.h
   libr-icons.h
   libr-i18n.h
-  libr-gtk.h
   libr.h
 )
 
+if( WITH_GTK )
+  list( APPEND ${target}_INCLUDES libr-gtk.h )
+endif( WITH_GTK )
+
 install(
   FILES ${${target}_INCLUDES}
   DESTINATION ${INCLUDE_INSTALL_DIR}/libr