directfb: disable for musl toolchains

Fixes:
http://autobuild.buildroot.net/results/548/548bf7b800a946e97135c0ba66363f388e517d6f/

Directfb doesn't build with musl, and upstream seems dead - So just disable
it.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/directfb/Config.in

@@ -3,6 +3,7 @@ config BR2_PACKAGE_DIRECTFB
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_5
+	depends on !BR2_TOOLCHAIN_USES_MUSL # sigval_t issue
 	select BR2_PACKAGE_FREETYPE
 	select BR2_PACKAGE_ZLIB
 	help
@@ -164,5 +165,6 @@ config BR2_PACKAGE_DIRECTFB_TESTS
 
 endif # BR2_PACKAGE_DIRECTFB
 
-comment "directfb needs a toolchain w/ C++, threads, gcc >= 4.5"
-	depends on !BR2_TOOLCHAIN_HAS_THREADS || !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_GCC_AT_LEAST_4_5
+comment "directfb needs a (e)glibc or uClibc toolchain w/ C++, threads, gcc >= 4.5"
+	depends on !BR2_TOOLCHAIN_HAS_THREADS || !BR2_INSTALL_LIBSTDCPP || \
+		!BR2_TOOLCHAIN_GCC_AT_LEAST_4_5 || BR2_TOOLCHAIN_USES_MUSL