Set OS X Deployment Target to 10.9 to match Swift

Swift builds its dylibs with an OS X Deployment Target of 10.9. Our Xcode project should do so as well.

Author: eschaton

XCTest.xcodeproj/project.pbxproj

@@ -361,7 +361,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				MACOSX_DEPLOYMENT_TARGET = 10.11;
+				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = macosx;
@@ -402,7 +402,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				MACOSX_DEPLOYMENT_TARGET = 10.11;
+				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = macosx;
 				VERSIONING_SYSTEM = "apple-generic";