libvips: requires C++ support

libvips requires C++ support, otherwise it will fail with an error
message like this one:

error: ../libvips/.libs/libvips.so: No such file or directory

The '--disable-cxx' configure option seems to be broken, so in the
meantime a compiler with C++ support is required in order to build
libvips successfully.

Reported upstream:

  https://github.com/jcupitt/libvips/issues/231

Fixes:

  http://autobuild.buildroot.net/results/cdc7cf5d3501f80c74b70aa09f93b2ad4e2f8602/
  http://autobuild.buildroot.net/results/39173dbcbbd0a243900ea583cec024b51f8b803a/
  http://autobuild.buildroot.net/results/6794705195bcdb636a8e6582ef5a1e153d4d66b3/

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libvips/Config.in

@@ -3,6 +3,9 @@ config BR2_PACKAGE_LIBVIPS
 	depends on BR2_USE_WCHAR # gettext, libglib2
 	depends on BR2_TOOLCHAIN_HAS_THREADS # libglib2
 	depends on BR2_USE_MMU # fork()
+	# C++ support is required to build libvips
+	# https://github.com/jcupitt/libvips/issues/231
+	depends on BR2_INSTALL_LIBSTDCPP
 	select BR2_PACKAGE_LIBGLIB2
 	select BR2_PACKAGE_LIBXML2
 	select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT_IF_LOCALE
@@ -13,6 +16,7 @@ config BR2_PACKAGE_LIBVIPS
 
 	  http://www.vips.ecs.soton.ac.uk/
 
-comment "libvips needs a toolchain w/ wchar, threads"
+comment "libvips needs a toolchain w/ wchar, threads, C++"
         depends on BR2_USE_MMU
-        depends on !BR2_USE_WCHAR || !BR2_TOOLCHAIN_HAS_THREADS
+        depends on !BR2_USE_WCHAR || !BR2_TOOLCHAIN_HAS_THREADS || \
+		!BR2_INSTALL_LIBSTDCPP

package/libvips/libvips.mk

@@ -33,11 +33,9 @@ LIBVIPS_DEPENDENCIES = \
 	host-pkgconf libglib2 \
 	libxml2 $(if $(BR2_NEEDS_GETTEXT_IF_LOCALE),gettext)
 
-ifeq ($(BR2_INSTALL_LIBSTDCPP),y)
+# --disable-cxx is broken upstream
+# https://github.com/jcupitt/libvips/issues/231
 LIBVIPS_CONF_OPTS += --enable-cxx
-else
-LIBVIPS_CONF_OPTS += --disable-cxx
-endif
 
 ifeq ($(BR2_PACKAGE_JPEG),y)
 LIBVIPS_CONF_OPTS += --with-jpeg