package/imagemagick: SVG support needs host gcc >= 4.9

SVG support needs host gcc >= 4.9 since bump of harfbuzz to version
3.1.2 in commit 6861933d22006fbe8c961a41506beac826881f33:

In file included from ../src/hb.hh:473:0,
                 from ../src/hb-buffer-serialize.cc:27:
../src/hb-vector.hh:206:20: error: 'is_trivially_copy_assignable' is not a member of 'std'
      hb_enable_if (std::is_trivially_copy_assignable<T>::value)>
                    ^

Fixes:
 - http://autobuild.buildroot.org/results/7b2430c5ae4eed51685ec12bf778c07a0a8b1701

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/imagemagick/Config.in.host

@@ -17,6 +17,7 @@ if BR2_PACKAGE_HOST_IMAGEMAGICK
 config BR2_PACKAGE_HOST_IMAGEMAGICK_SVG
 	bool "SVG support"
 	depends on BR2_PACKAGE_HOST_RUSTC_ARCH_SUPPORTS # host-librsvg
+	depends on BR2_HOST_GCC_AT_LEAST_4_9 # host-pango -> host-harfbuzz
 	help
 	  Say 'y' here is you need ImageMagick tools (like convert)
 	  to support SVG.
@@ -24,4 +25,8 @@ config BR2_PACKAGE_HOST_IMAGEMAGICK_SVG
 	  This is not enabled by default, as it brings quite a few
 	  extra dependencies, and thus extra build time.
 
+comment "SVG support needs host gcc >= 4.9"
+	depends on BR2_PACKAGE_HOST_RUSTC_ARCH_SUPPORTS
+	depends on !BR2_HOST_GCC_AT_LEAST_4_9
+
 endif