toolchain/internal: check kernel headers version for manually-specified version

Ensure the kernel headers version matches exactly the one manually
specified by the user.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linux-headers/linux-headers.mk

@@ -37,4 +37,13 @@ define LINUX_HEADERS_INSTALL_STAGING_CMDS
 			headers_install)
 endef
 
+ifeq ($(BR2_KERNEL_HEADERS_VERSION),y)
+define LINUX_HEADERS_CHECK_VERSION
+	$(call check_kernel_headers_version,\
+		"$(TARGET_CC) $(TOOLCHAIN_EXTERNAL_CFLAGS)",\
+		$(call qstrip,$(BR2_TOOLCHAIN_HEADERS_AT_LEAST)))
+endef
+LINUX_HEADERS_POST_INSTALL_STAGING_HOOKS += LINUX_HEADERS_CHECK_VERSION
+endif
+
 $(eval $(generic-package))