[source] kernel: speed up build system by getting rid of redundant work

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/1f12a3daaaa8f3525741bef2bc2be7c5c6c77b50

commit 1f12a3daaaa8f3525741bef2bc2be7c5c6c77b50
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Mar 16 09:33:18 2017 +0100

    kernel: speed up build system by getting rid of redundant work
    
    KERNELRELEASE contains a $(shell) call which is evaluated over and over
    again.
    The call to checksyscalls.sh is unnecessary for LEDE and also takes a
    few seconds to complete.
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/kernel-defaults.mk | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/kernel-defaults.mk b/include/kernel-defaults.mk
index 10bd67a..1c3b428 100644
--- a/include/kernel-defaults.mk
+++ b/include/kernel-defaults.mk
@@ -23,7 +23,9 @@ KERNEL_MAKEOPTS := -C $(LINUX_DIR) \
 	HOST_LOADLIBES="-L$(STAGING_DIR_HOST)/lib" \
 	CONFIG_SHELL="$(BASH)" \
 	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='') \
-	$(if $(PKG_BUILD_ID),LDFLAGS_MODULE=--build-id=0x$(PKG_BUILD_ID))
+	$(if $(PKG_BUILD_ID),LDFLAGS_MODULE=--build-id=0x$(PKG_BUILD_ID)) \
+	KERNELRELEASE=$(LINUX_VERSION) \
+	cmd_syscalls=
 
 ifdef CONFIG_STRIP_KERNEL_EXPORTS
   KERNEL_MAKEOPTS += \