Fix funcret regvar relocation across inlined blocks hiding `fc_exit` #41558

Fibonaccirequested to merge
fibodevy/fpc-source:fix-#41558 into main

Fixes #41558

i386 -Ooregvar bug: Result-regvar relocation inside an inlined block skipped by an earlier exit, epilogue reads the new reg and returns garbage. Guard in do_replace_node_regs relied on fc_exit, which nf_block_with_exit blocks clear. Fix just pins the funcret sym's localloc - rest is in the code comment.

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