Remove the comptime_flat/need_vm gate and the vm_result-orelse-legacy
fallback from emit_llvm.zig (runComptimeSideEffects + emitGlobals const-init)
and comptime.zig (runComptimeTypeFunc). The comptime VM now always runs;
a bail is always a build-gating diagnostic, never a fallback. Delete the
now-moot entryNeedsVm. runComptimeSideEffects drops the Interpreter entirely
(VM writes #run output direct to fd 1); emitGlobals keeps a fresh interp_inst
only as the valueToLLVMConst materialization context (the regToValue bridge,
removed with interp.zig in a later step).
#insert (evalComptimeString) still routes through the legacy interp — deferred
until interp.zig deletion.
Reconcile 1654: the comptime asm-global #run now reports the VM's clean dlsym
bail instead of the legacy CannotEvalComptime wrapper (exit still 1).
501/501 unit + 706/0 corpus.
Adds examples/1654-platform-asm-global-comptime-call.sx — the comptime
guard. A module-asm symbol only exists after assemble+link; the comptime
interpreter resolves extern calls via host dlsym, where it's absent, so
`#run my_add(…)` fails with a clear diagnostic ("comptime extern call:
symbol not found via dlsym") rather than misfiring. Runtime calls work
(1648/1653). dlsym-miss precedes asm assembly, so arch-independent — no
.build. Locks current behavior; no compiler change.
