qt5base: use system/buildroot provided freetype

Select (and use) builroot provided freetype in case qt5base gui is
selected (gui without freetype/font support makes not much sense
and gives compile errors).

Qt 5.6 needs some support to find the include headers, 5.8 is
clever enough inherently.

Fixes [1] (by avoiding the build-in freetype library which depends
on activated libpng support):

  Project ERROR: Library 'libpng' is not defined.
  make[3]: *** [sub-3rdparty-freetype-make_first] Error 3

[1] http://autobuild.buildroot.net/results/219162ba616289f799a5053c4dcc6b8574284283

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/qt5/qt5base/Config.in

@@ -128,6 +128,7 @@ config BR2_PACKAGE_QT5BASE_XML
 
 config BR2_PACKAGE_QT5BASE_GUI
 	bool "gui module"
+	select BR2_PACKAGE_FREETYPE
 	# At least one graphic backend must be enabled, so enable
 	# linuxfb if nothing is enabled.
 	select BR2_PACKAGE_QT5BASE_LINUXFB if \

package/qt5/qt5base/qt5base.mk

@@ -97,7 +97,13 @@ QT5BASE_DEPENDENCIES   += $(if $(BR2_PACKAGE_QT5BASE_SQLITE_SYSTEM),sqlite)
 QT5BASE_CONFIGURE_OPTS += $(if $(BR2_PACKAGE_QT5BASE_SQLITE_NONE),-no-sql-sqlite)
 endif
 
-QT5BASE_CONFIGURE_OPTS += $(if $(BR2_PACKAGE_QT5BASE_GUI),-gui,-no-gui)
+ifeq ($(BR2_PACKAGE_QT5BASE_GUI),y)
+QT5BASE_CONFIGURE_OPTS += -gui -system-freetype
+QT5BASE_CONFIGURE_OPTS += $(if $(BR2_PACKAGE_QT5_VERSION_5_6),-I$(STAGING_DIR)/usr/include/freetype2)
+QT5BASE_DEPENDENCIES += freetype
+else
+QT5BASE_CONFIGURE_OPTS += -no-gui -no-freetype
+endif
 QT5BASE_CONFIGURE_OPTS += $(if $(BR2_PACKAGE_QT5BASE_WIDGETS),-widgets,-no-widgets)
 # We have to use --enable-linuxfb, otherwise Qt thinks that -linuxfb
 # is to add a link against the "inuxfb" library.