We've always cached kernel compiles during bundle builds. This adds
caching for kernel compiles during AOT builds by moving caching into the
KernelCompiler.compile() method rather than around each invocation of it.

This also filters buildbot paths included by the kernel compile that are
not present on the local machine at paths /b/build/slave/Linux_Engine/...
The kernel compiler should probably include an option to not emit these
paths in the depfile, since these are used both by Gradle and the
Fingerprinter class.