package/janet: needs gcc >= 4.9

janet needs gcc >= 4.9 for stdatomic.h since version 1.26.0 and
https://github.com/janet-lang/janet/commit/bfcfd58259911b92ff516bab9216831b34653805
resulting in the following build failure since commit
5c6f32bd255fc97823d464beacfa905a141066ec:

src/core/abstract.c:35:23: fatal error: stdatomic.h: No such file or directory

Fixes:
 - http://autobuild.buildroot.org/results/a2b40adb93b751221ba2cdf9a705f86c30499021

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/janet/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_JANET
 	bool "janet"
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_9 # C11/stdatomic.h
 	help
 	  Janet is a functional and imperative programming language.
 	  The entire language (core library, interpreter, compiler,
@@ -8,3 +9,6 @@ config BR2_PACKAGE_JANET
 	  and two headers.
 
 	  https://janet-lang.org/
+
+comment "janet needs a toolchain w/ gcc >= 4.9"
+	depends on !BR2_TOOLCHAIN_GCC_AT_LEAST_4_9