lua-curl-v3: fix build on macos

lua-curl-v3 detects OS and changes compilation flags depends on OS.
If Darwin is detected then it adds GCC non-compatible flags.
OpenWrt is always Linux, OS detection is disabled via UNAME=Linux
as a part of MAKE_FLAGS

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>

lang/lua-curl-v3/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=lua-curl-v3
 PKG_VERSION:=0.3.13-snapshot
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_LICENSE:=MIT
 PKG_LICENSE_FILES:=LICENSE
 
@@ -29,6 +29,9 @@ define Package/lua-curl-v3
     MAINTAINER:=Rainer Poisel <rainer.poisel@gmail.com>
 endef
 
+MAKE_FLAGS += \
+	UNAME="Linux"
+
 define Package/lua-curl-v3/description
 	Lua bindings to libcurl (Lua-cURLv3)
 endef