tvheadend: Fix compilation on GCC8

New string warnings were introduced. Adding -Wno-error to TARGET_CFLAGS
does not work so patch it out.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry-picked from 9eea417e92)

multimedia/tvheadend/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=tvheadend
 PKG_VERSION:=4.0.10
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/tvheadend/tvheadend/tar.gz/v$(PKG_VERSION)?
@@ -72,8 +72,6 @@ CONFIGURE_ARGS += \
 	--disable-libav \
 	--enable-bundle
 
-TARGET_CFLAGS += -Wno-error=pointer-compare
-
 define Build/Prepare
 	$(call Build/Prepare/Default)
 	echo 'Tvheadend $(shell echo $(PKG_SOURCE_VERSION) | sed "s/^v//")~openwrt$(PKG_RELEASE)' \