Merge pull request swiftlang#146 from ahoppen/ignore-temp-xcode-files

Ignore any files Xcode generates when the package is opened directly

Author: ahoppen

.gitignore

@@ -2,6 +2,8 @@
 .build/
 # Ignore generated Xcode projects
 *.xcodeproj
+# Ignore Data Xcode stores when opening the project directly
+/.swiftpm/xcode
 
 # We always build swiftSyntax of master dependencies. Ignore any fixed 
 # dependency versions.