Add coverage gitignore.

.gitignore

@@ -1,3 +1,4 @@
+# C++.gitignore
 # Prerequisites
 *.d
 
@@ -30,3 +31,10 @@
 *.exe
 *.out
 *.app
+
+# Gcov.gitignore
+# gcc coverage testing tool files
+
+*.gcno
+*.gcda
+*.gcov