toolchain/kernel-headers: don't use TARGET_CFLAGS

Kernel utilities (e.g. scripts/kconfig/conf) are being built to run on
the host system at this stage, therefore it makes no sense to use the
target system CC flags.  Use HOSTCFLAGS instead

While we're here rename KMAKE macro to HOST_KMAKE to make it even more
obvious that we're building for host.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

toolchain/kernel-headers/Makefile

@@ -41,14 +41,14 @@ HOST_EXTRACFLAGS=
 
 LINUX_HAS_HEADERS_INSTALL:=y
 
-KMAKE := $(MAKE) -C $(HOST_BUILD_DIR) \
+HOST_KMAKE := $(MAKE) -C $(HOST_BUILD_DIR) \
 	$(KERNEL_MAKE_FLAGS) \
 	CC="$(KERNEL_CC)" \
-	CFLAGS="$(TARGET_CFLAGS)"
+	HOSTCFLAGS="$(HOST_CFLAGS)"
 
 define Host/Configure/all
 	mkdir -p $(BUILD_DIR_TOOLCHAIN)/linux-dev
-	$(KMAKE) \
+	$(HOST_KMAKE) \
 		INSTALL_HDR_PATH="$(BUILD_DIR_TOOLCHAIN)/linux-dev/" \
 		headers_install
 endef
@@ -82,7 +82,7 @@ endef
 
 define Host/Configure
 	env
-	yes '' | $(KMAKE) oldconfig
+	yes '' | $(HOST_KMAKE) oldconfig
 	$(call Host/Configure/all)
 	$(call Host/Configure/post/$(ARCH))
 endef