Bug 24413 – ImportC: undefined identifier `__builtin_unreachable`

Reported from NewsGroup: https://forum.dlang.org/post/[email protected] No other information in post other than the identifier is missing ``__builtin_unreachable``.

Found something to reproduce it. While trying to compile <https://github.com/mity/md4c/blob/481fbfbdf72daab2912380d62bb5f2187d438408/src/md4c.c>, I ended up with this wall of errors: md4c.c(1084,43): Error: undefined identifier `__builtin_unreachable` md4c.c(1235,43): Error: undefined identifier `__builtin_unreachable` md4c.c(1308,43): Error: undefined identifier `__builtin_unreachable` md4c.c(1383,34): Error: undefined identifier `__builtin_unreachable` md4c.c(2293,72): Error: undefined identifier `__builtin_unreachable` md4c.c(2294,45): Error: undefined identifier `__builtin_unreachable` md4c.c(2357,43): Error: undefined identifier `__builtin_unreachable` md4c.c(2564,23): Error: undefined identifier `__builtin_unreachable` md4c.c(2574,23): Error: undefined identifier `__builtin_unreachable` md4c.c(2594,23): Error: undefined identifier `__builtin_unreachable` md4c.c(2663,33): Error: undefined identifier `__builtin_unreachable` md4c.c(2666,56): Error: undefined identifier `__builtin_unreachable` md4c.c(2675,33): Error: undefined identifier `__builtin_unreachable` md4c.c(2903,43): Error: undefined identifier `__builtin_unreachable` md4c.c(2931,43): Error: undefined identifier `__builtin_unreachable` md4c.c(2942,43): Error: undefined identifier `__builtin_unreachable` md4c.c(3613,62): Error: undefined identifier `__builtin_unreachable` md4c.c(3617,62): Error: undefined identifier `__builtin_unreachable` md4c.c(3692,40): Error: undefined identifier `__builtin_unreachable` md4c.c(3725,43): Error: undefined identifier `__builtin_unreachable` (Importing the header only appears to be working fine.)

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