gitignore: ignore gcov output files

Ignore *.gcno files which are generated by gcov.
Signed-off-by: NWANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

.gitignore

@@ -27,6 +27,7 @@
 *.gz
 *.lzma
 *.patch
+*.gcno
 
 #
 # Top-level generic files