Companion to bincraft codefloe #65. Sets `BINCRAFT_VERBOSE_PATCH_BUILD=TRUE` in the trial-build gate so a failed isolated patched build prints the real compiler error instead of `System command 'R' failed`. Harmless on bincraft versions without the flag (unknown env var is ignored). Takes effect once bincraft #65 is released and the build-env images pick it up.
Reviewed-on: #129