toolchain: glibc: Define minimum support kernel version as 4.14

This will compile glibc in a way that it will only support kernel 4.14
and later. Compatibility code for older kernel versions will be removed.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

toolchain/glibc/common.mk

@@ -60,7 +60,8 @@ GLIBC_CONFIGURE:= \
 		--without-gd \
 		--without-cvs \
 		--enable-add-ons \
-		--$(if $(CONFIG_SOFT_FLOAT),without,with)-fp
+		--$(if $(CONFIG_SOFT_FLOAT),without,with)-fp \
+		--enable-kernel=4.14.0
 
 export libc_cv_ssp=no
 export libc_cv_ssp_strong=no