[Bug rtl-optimization/79856] rtl_verify_edges: use internal_error instead of error

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79856

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note that internal_error will terminate GCC immediately while error () allows
for further errors to be diagnosed.  Which is what we want here, internal_error
is done as the final step in "CFG verification failed" or so.