directfb: disable for sparc

Requires atomic operations.
Fixes following autobuild failure:
http://autobuild.buildroot.net/results/8205100c166659c47daff66b1e63edc82eeb7930/

[Peter: also hide toolchain comment]
Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/directfb/Config.in

@@ -4,6 +4,7 @@ config BR2_PACKAGE_DIRECTFB
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_5
 	depends on !BR2_TOOLCHAIN_USES_MUSL # sigval_t issue
+	depends on !BR2_sparc # needs atomic operation __sync_fetch_and_add
 	select BR2_PACKAGE_FREETYPE
 	select BR2_PACKAGE_ZLIB
 	help
@@ -166,5 +167,6 @@ config BR2_PACKAGE_DIRECTFB_TESTS
 endif # BR2_PACKAGE_DIRECTFB
 
 comment "directfb needs a (e)glibc or uClibc toolchain w/ C++, threads, gcc >= 4.5"
+	depends on !BR2_sparc # needs atomic operation __sync_fetch_and_add
 	depends on !BR2_TOOLCHAIN_HAS_THREADS || !BR2_INSTALL_LIBSTDCPP || \
 		!BR2_TOOLCHAIN_GCC_AT_LEAST_4_5 || BR2_TOOLCHAIN_USES_MUSL