gitignore: ignore gcov output files

Ignore *.gcno files which are generated by gcov.

Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/.gitignore b/.gitignore
index cecb3b0..b93fb7e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -27,6 +27,7 @@
 *.gz
 *.lzma
 *.patch
+*.gcno
 
 #
 # Top-level generic files