package/libuhttpd: depends on gcc >= 4.9

Add a dependency on gcc >= 4.9 to avoid the following build failure
with gcc 4.8.3 raised since bump to version 3.14.1 in commit
61797c52f5deef2cb67e60cf075ca243078c8855 and
https://github.com/zhaojh329/libuhttpd/commit/ffdf7de3a4a1f5a62aa3814ac96e889958a30840:

/home/peko/autobuild/instance-1/output-1/build/libuhttpd-3.14.1/src/cgi.c:41:5: error: initializer element is not a constant expression [-Werror]
     {"accept", strlen("accept"), "HTTP_ACCEPT"},
     ^

It should be noted that upstream rejected a patch to remove -Werror:
https://github.com/zhaojh329/libuhttpd/pull/12

Fixes:
 - http://autobuild.buildroot.org/results/a3a970a6398dcb0e4e03f4277f1a50c6b5eff7bd

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

package/libuhttpd/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_LIBUHTTPD
 	bool "libuhttpd"
 	depends on BR2_USE_MMU # fork()
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_9
 	select BR2_PACKAGE_LIBEV
 	select BR2_PACKAGE_WOLFSSL_ALL if BR2_PACKAGE_WOLFSSL
 	help
@@ -8,3 +9,7 @@ config BR2_PACKAGE_LIBUHTTPD
 	  library based on libev
 
 	  https://github.com/zhaojh329/libuhttpd
+
+comment "libuhttpd needs a toolchain w/ gcc >= 4.9"
+	depends on BR2_USE_MMU
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_9