.gitignore: add .gcov pattern

The gcovr tool is very messy and can leave a lot of crap in the source
tree even when using build directories.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220204204335.1689602-5-alex.bennee@linaro.org>

.gitignore

@@ -15,3 +15,4 @@ GTAGS
 *.depend_raw
 *.swp
 *.patch
+*.gcov