add a few entries to .gitignore

- Development friendly files (tags, clang_complete)
- Cross-compile stuff (xgcc, tarballs)

This patch was originally written by Stefan.

Change-Id: I4229414c94ee04a4f38a748369c4ac90fda57aea
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-on: http://review.coreboot.org/2128
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

.gitignore

@@ -28,6 +28,7 @@ util/crossgcc/Python-*/
 util/crossgcc/tarballs/
 util/crossgcc/w32api-*/
 util/crossgcc/xgcc/
+
 *.\#
 *.bin
 *.debug
@@ -36,6 +37,14 @@ util/crossgcc/xgcc/
 *.out
 *.swp
 
+# Development friendly files
+tags
+.clang_complete
+
+# Cross-compile toolkits
+xgcc/
+tarballs/
+
 #
 # KDE editors create lots of backup files whenever
 # a file is edited, so just ignore them