.gitignore: .vscode/ipch directory

It seems an update has started make these C++ extension PCH files show up in version control.

Change-Id: I9af5dbf7e74bf8fb7d9ef25e84cce28b7424dda8
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27771
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <headlessclayton@gmail.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
diff --git a/.gitignore b/.gitignore
index 544ec62..6362020 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,7 @@
 /bin/
 /out/
 .vs
+.vscode/ipch
 CMakeFiles/
 
 # The /build/ directory is recommended for CMake build output and should be