Use plain xcodebuild instead of xctool

xctool won't support Xcode 8 and will be deprecated.

.travis.yml

@@ -1,6 +1,3 @@
-before_install:
-  - brew update
-  - brew outdated xctool || brew upgrade xctool
 install: true
 git:
   submodules: false
@@ -30,7 +27,6 @@ notifications:
     secure: lblNhCx6581hiPskQQnH663QY/HHqs6y8rMCLIff1Ryq0ngBaTwBJZ6E5tAR8oWTGWg3nMAAm/AaJPQGFC9jnKxtpWJhuEF58RY+EBe1Rz3gjKmacvEZS+PW+k3cRrRPZr6Vh6D8d0cb1gfM7BvGZar21ipBC/WcnNden3LxZ+0=
 env:
   global:
-    - BUILD_TOOL=xctool
     - secure: DofNs+Ej7JblkkGMTHOl4XMBfv0EKVvzZU7OOm7U6Hyxu0J0SN6E3s61Q4HUWOBvM3Yrxf+8jpFKI29w69WArmRPpmK6GCaZar8ldUBHNmN3gaeOaGmGyrmnre4hxHjJzc0E3HAmJ03v94HW5JwQzKpIUjxg4dSttJMT6WOmnxE=
 deploy:
   provider: releases

Makefile

@@ -1,6 +1,5 @@
 TEMPORARY_FOLDER?=/tmp/Carthage.dst
 PREFIX?=/usr/local
-BUILD_TOOL?=xcodebuild
 
 XCODEFLAGS=-workspace 'Carthage.xcworkspace' -scheme 'carthage' DSTROOT=$(TEMPORARY_FOLDER)
 
@@ -21,19 +20,19 @@ COMPONENTS_PLIST=Source/carthage/Components.plist
 .PHONY: all bootstrap clean install package test uninstall
 
 all: bootstrap
-	$(BUILD_TOOL) $(XCODEFLAGS) build
+	xcodebuild $(XCODEFLAGS) build
 
 bootstrap:
 	git submodule update --init --recursive
 
 test: clean bootstrap
-	$(BUILD_TOOL) $(XCODEFLAGS) test
+	xcodebuild $(XCODEFLAGS) test
 
 clean:
 	rm -f "$(OUTPUT_PACKAGE)"
 	rm -f "$(OUTPUT_FRAMEWORK_ZIP)"
 	rm -rf "$(TEMPORARY_FOLDER)"
-	$(BUILD_TOOL) $(XCODEFLAGS) clean
+	xcodebuild $(XCODEFLAGS) clean
 
 install: package
 	sudo installer -pkg Carthage.pkg -target /
@@ -43,7 +42,7 @@ uninstall:
 	rm -f "$(BINARIES_FOLDER)/carthage"
 
 installables: clean bootstrap
-	$(BUILD_TOOL) $(XCODEFLAGS) install
+	xcodebuild $(XCODEFLAGS) install
 
 	mkdir -p "$(TEMPORARY_FOLDER)$(FRAMEWORKS_FOLDER)" "$(TEMPORARY_FOLDER)$(BINARIES_FOLDER)"
 	mv -f "$(CARTHAGEKIT_BUNDLE)" "$(TEMPORARY_FOLDER)$(FRAMEWORKS_FOLDER)/$(OUTPUT_FRAMEWORK)"