Add missing .gitignore entries for VS2015 IntelliSense DB (#1223)

diff --git a/.gitignore b/.gitignore
index 8b54c2c..f436777 100644
--- a/.gitignore
+++ b/.gitignore
@@ -54,6 +54,8 @@
 PCbuild/*.*sdf
 PCbuild/*-pgi
 PCbuild/*-pgo
+PCbuild/*.VC.db
+PCbuild/*.VC.opendb
 PCbuild/.vs/
 PCbuild/amd64/
 PCbuild/obj/