Disable ccache when using mingw.

Change-Id: I40ec9f6dfbf54b362b8a87cde7774b396b46b063
diff --git a/build/tools/windows_sdk.mk b/build/tools/windows_sdk.mk
index 91033a6..7e1b541 100644
--- a/build/tools/windows_sdk.mk
+++ b/build/tools/windows_sdk.mk
@@ -76,7 +76,7 @@
 
 winsdk-tools: $(WIN_BUILD_PREREQ)
 	$(call winsdk-banner,Build Windows Tools)
-	$(hide) USE_MINGW=1 $(MAKE) PRODUCT-$(TARGET_PRODUCT)-$(strip $(WIN_TARGETS)) $(if $(hide),,showcommands)
+	$(hide) USE_MINGW=1 USE_CCACHE="" $(MAKE) PRODUCT-$(TARGET_PRODUCT)-$(strip $(WIN_TARGETS)) $(if $(hide),,showcommands)
 
 $(WIN_SDK_ZIP): winsdk-tools sdk
 	$(call winsdk-banner,Build $(WIN_SDK_NAME))