toolchain: add 4.0.x choice for headers

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/toolchain/toolchain-common.in b/toolchain/toolchain-common.in
index 13c684d..1b25cf1 100644
--- a/toolchain/toolchain-common.in
+++ b/toolchain/toolchain-common.in
@@ -222,10 +222,15 @@
 	bool
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_18
 
+config BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_0
+	bool
+	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_19
+
 # This order guarantees that the highest version is set, as kconfig
 # stops affecting a value on the first matching default.
 config BR2_TOOLCHAIN_HEADERS_AT_LEAST
 	string
+	default "4.0"  if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_0
 	default "3.19" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_19
 	default "3.18" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_18
 	default "3.17" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_17