toolchain: add musl libc.so to external toolchain

musl provides a /lib/libc.so file which should be integrated into the libc
package when the external toolchain with musl is used.

Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Jo-Philipp Wich <jo@mein.io>

package/libs/toolchain/Makefile

@@ -164,7 +164,7 @@ define Package/libc/config
 		string
 		prompt "libc shared library files (use wildcards)"
 		depends on EXTERNAL_TOOLCHAIN && PACKAGE_libc
-		default "./lib/ld{*.so*,-linux*.so.*} ./lib/lib{anl,c,cidn,crypt,dl,m,nsl,nss_dns,nss_files,resolv,util}{-*.so,.so.*}"
+		default "./lib/ld{*.so*,-linux*.so.*} ./lib/lib{anl,c,cidn,crypt,dl,m,nsl,nss_dns,nss_files,resolv,util}{-*.so,.so.*,.so}"
 
 	endmenu
 endef