build: exempt download-only make goals from the gfortran check (#62695)
Make.inc errors at parse time for any `USE_BINARYBUILDER=0` make when no
functioning fortran compiler is found, including invocations that never
run a compiler at all: `make -C stdlib getall USE_BINARYBUILDER=0` (run
by `light-source-dist` to vendor the stdlib source tarballs), `make -C
deps getall`, and the source-dist targets themselves. Skip the check
when every requested goal only downloads or repackages sources; a
default-goal build (empty `MAKECMDGOALS`) still errors early as
intended.
This surfaced in the CI source-dist step (JuliaCI/julia-buildkite#597),
whose rootfs has no gfortran; with this change the `FC=gcc` workaround
there can eventually be dropped.
Verified behavior without a fortran compiler (`FC=no-such-fortran`):
- `make -C stdlib getall USE_BINARYBUILDER=0`: now parses and runs
(previously errored)
- `make -C deps getall USE_BINARYBUILDER=0`: now parses and runs
(previously errored)
- `make USE_BINARYBUILDER=0` (default build): still errors early
- `make -C deps compile-openblas USE_BINARYBUILDER=0`: still errors
early
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit bb79ec882e15bb8e333172648a5e8b1f01bc6e8b)