Warn when a call name matches in BOTH the Pascal and C namespaces

• Track: A (FindProc / symtab) with C-frontend touch. Rainy-day.
• Opened: 2026-07-19, side effect of the two-libm approach (feature-crtl-libm-correctly-rounded-transcendentals).

The case-insensitive C/Pascal proc namespace is what made a C exp definition next to Pascal Exp silently break call binding (b377 — the argument never arrived). The crtl fix (__crtl_ names + macros) removes the collisions we know about, but the FAILURE MODE is still silent for the next one.

Proposal (user sketch):

1. Deterministic search order by source language: a call from Pascal source resolves Pascal RTL first; a call from C source resolves crtl/C procs first. (Largely true today by accident of registration order — make it explicit.)
2. Compiler warning when more than one candidate matches a call across the namespaces (differing only by case / origin), so the next exp/Exp pair is loud instead of silent garbage.
3. Same idea one level up: warn when multiple units in the search path provide the same routine name.

Minor, diagnostics-only — no behavior change without a decide. Gate: warning fires on a synthetic exp/Exp twin, quiet on the normal corpus builds.