Disable CCACHE_DIRECT for kernel builds

Disable CCACHE_DIRECT so that header location changes are
actually noticed.

BUG=none
Change-Id: I51f601c869fa28265e961ffe0aa64428ea204391
Signed-off-by: Stefan Stanacar <stefan.stanacar@intel.com>
diff --git a/kernel.mk b/kernel.mk
index 7721186..fead062 100644
--- a/kernel.mk
+++ b/kernel.mk
@@ -156,7 +156,8 @@
 $(KERNEL_BIN): $(KERNEL_OUT) $(KERNEL_CONFIG)
 	$(hide) echo "Building $(KERNEL_ARCH) $(KERNEL_VERSION) kernel..."
 	$(hide) rm -rf $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/dts
-	$(MAKE) -C $(TARGET_KERNEL_SRC) O=$(realpath $(KERNEL_OUT)) ARCH=$(KERNEL_ARCH) CROSS_COMPILE="$(KERNEL_CROSS_COMPILE_WRAPPER)" KCFLAGS="$(KERNEL_CFLAGS)" KAFLAGS="$(KERNEL_AFLAGS)"
+	# Disable CCACHE_DIRECT so that header location changes are noticed.
+	CCACHE_NODIRECT="true" $(MAKE) -C $(TARGET_KERNEL_SRC) O=$(realpath $(KERNEL_OUT)) ARCH=$(KERNEL_ARCH) CROSS_COMPILE="$(KERNEL_CROSS_COMPILE_WRAPPER)" KCFLAGS="$(KERNEL_CFLAGS)" KAFLAGS="$(KERNEL_AFLAGS)"
 	$(MAKE) -C $(TARGET_KERNEL_SRC) O=$(realpath $(KERNEL_OUT)) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) headers_install;
 
 # If the kernel generates VDSO files, generate breakpad symbol files for them.