dump1090: Support cross-compiling (from OS X)

dump1090 doesn't detect cross-compilation; instead, they check uname.
For OpenWrt, the target will always be Linux, so just forcibly set it.

Signed-off-by: Mike Miller <github@mikeage.net>

utils/dump1090/Makefile

@@ -1,5 +1,5 @@
 #
-# Copyright (C) 2013-2015 OpenWrt.org
+# Copyright (C) 2013-2016 OpenWrt.org
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=dump1090
 PKG_VERSION:=2015-11-22
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=git://github.com/mutability/dump1090.git
@@ -53,7 +53,8 @@ define Package/view1090/description
 endef
 
 MAKE_FLAGS += \
-	CFLAGS="$(TARGET_CFLAGS)"
+	CFLAGS="$(TARGET_CFLAGS)" \
+	UNAME=Linux
 
 define Package/dump1090/install
 	$(INSTALL_DIR) $(1)/etc/init.d