[clang] [clang][MBD] set up module build daemon infrastructure (PR #67562)

[Connor Sughrue via cfe-commits]

================
@@ -0,0 +1,18 @@
+// Check that clang invocation can spawn and handshake with module build daemon
+
+// REQUIRES: !system-windows
+
+//  RUN: if pgrep -f "cc1modbuildd mbd-handshake"; then pkill -f "cc1modbuildd mbd-handshake"; fi
+//  RUN: rm -rf mbd-handshake %t
----------------
cpsughrue wrote:

I could also set up the client to have a max length of 108 too which would guarantee they always match.

https://github.com/llvm/llvm-project/pull/67562