Suppressing the number of a constant-evaluation notes is an internal error: "determine_severity_code: bad severity" #405

Issue Summary

When constant evaluation fails in C++, the error "expression must have a constant value" (#28) carries the
interpreter's diagnostics as notes, for example "shift count is too large" (#63), "shift count is negative" (#62),
"division by zero" (#39) and "integer operation result is out of range" (#61). Each note is created as an
es_more_info diagnostic, and create_diagnostic_entry (error.c) applies check_for_overridden_severity to it as
to any other diagnostic. With --diag_suppress (or #pragma diag_suppress) naming a note's number, the note gets
severity es_none. Displaying the error then reaches determine_severity_code with es_none (error.c line 3023)
and stops with an internal error. It happens in the C++ constant-expression contexts that report through error #28:
a constexpr variable, an enumerator, static_assert, an array bound, a template argument, if constexpr,
alignas, a bit-field width (not a case label, which reports #39 itself, and not a narrowing template argument,
#2361). Only the text output fails: the SARIF output (--output_mode=sarif) does not compute a note's severity and
lists the suppressed note as a related location. C has no such notes and is not affected.

Reproducing Source Code

constexpr int z = 1 << 32;

Command-line Options

cpfe --c++20 --diag_suppress=63 shift.cpp

Type of Issue

[Front End] This code SHOULD compile with these options.

Additional Details

Output of at current main:

"shift.cpp", line 1: internal error: assertion failed:
          determine_severity_code: bad severity (error.c, line 3023 in
          determine_severity_code)

  constexpr int z = 1 << 32;
                    ^

1 error and 1 catastrophic error detected in the compilation of "shift.cpp".
Compilation aborted.

Reproducing (Standard) Configuration(s)

No response

Reproducing (Non-standard) Configuration

No response

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