strip path when untaring kernel for headers

This is needed when custom/snapshot kernel headers are selected.
Buildroot expects to find dl/linux-2.6.tar.bz2 and also expects
it to extract to output/toolchain/linux-2.6, but if you tar
custom kernel sources directory can be anything, etc. linux-git.
In that case buildroot would extract it to output/toolchain/linux-git.
So fix this behaviour, by using tar strip-directory/component.

Signed-off-by: Paulius Zaleckas <paulius.zaleckas@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/kernel-headers/kernel-headers-new.makefile

@@ -28,8 +28,9 @@ LINUX_HEADERS_DEPENDS:=
 $(LINUX_HEADERS_UNPACK_DIR)/.unpacked: $(DL_DIR)/$(LINUX_HEADERS_SOURCE)
 	@echo "*** Using kernel-headers generated from kernel source"
 	rm -rf $(LINUX_HEADERS_DIR)
-	[ -d $(TOOLCHAIN_DIR) ] || $(INSTALL) -d $(TOOLCHAIN_DIR)
-	$(LINUX_HEADERS_CAT) $(DL_DIR)/$(LINUX_HEADERS_SOURCE) | tar -C $(TOOLCHAIN_DIR) $(TAR_OPTIONS) -
+	$(INSTALL) -d $(@D)
+	$(LINUX_HEADERS_CAT) $(DL_DIR)/$(LINUX_HEADERS_SOURCE) | \
+	tar $(TAR_STRIP_COMPONENTS)=1 -C $(@D) $(TAR_OPTIONS) -
 	touch $@
 
 $(LINUX_HEADERS_UNPACK_DIR)/.patched: $(LINUX_HEADERS_UNPACK_DIR)/.unpacked $(LINUX_HEADERS_DEPENDS)