spruce up .gitignore

Update gitignore to ignore additional temporary files and format more similar to
LLVM's .gitignore.

llvm-svn: 204111

lldb/.gitignore

@@ -1,4 +1,26 @@
+#==============================================================================#
+# The file specifies intentionally untracked files that git should ignore.
+# See: http://www.kernel.org/pub/software/scm/git/docs/gitignore.html
+#
+# This file is intentionally different from the output of `git svn show-ignore`,
+# as most of those are useless.
+#==============================================================================#
+
+#==============================================================================#
+# File extensions to be ignored anywhere in the tree.
+#==============================================================================#
+# Temp files created by most text editors.
+*~
+# Merge files created by git.
+*.orig
+# Byte compiled python modules.
 *.pyc
+# vim swap files
+.*.swp
+.sw?
+# OS X specific files.
+.DS_store
+
 build/
 llvm-build/
 *xcuserdata