runJITFromObject now takes priority dylibs (the #import c unit's
linked objects first, then #library deps in declaration order) and
attaches a per-path search generator for each AHEAD of the
process-wide fallback, so a vendored symbol can never lose to a
same-named export of an image the host process happens to carry
(libz via LLVM, libsqlite3 via CoreServices). loadLibrary reports
the name dlopen succeeded on; the c-import handle records its dylib
path; temp link inputs are per-pid so concurrent runs can't clobber
each other. Flips the C0.3 shadowing pin to from_unit: true.
