false positive cache hit on compiler_rt and libfuzzer when used via the build system

[andrewrk]

Zig Version

0.14.0-dev.569+4de8bba64

Steps to Reproduce and Observed Behavior

Use zig init to create a new project.

Build with zig build.

Make an edit to lib/compiler_rt.zig of the zig installation being used.

Run zig build again in the new project directory.

Observe that compiler_rt is not rebuilt.

Expected Behavior

The edits to compiler_rt.zig should be picked up.

In this case, the problem is that in Whole Cache Mode (used by the build system), the sub-compilation's source files do not make it into the cache manifest for the user application, so it does not check freshness of sub-compilation source files.

When a Compilation using Whole Cache Mode is working on a sub-Compilation, it must also add the child's file system inputs to the parent's cache manifest.