Migrate away from report_fatal_error

[kazutakahirata]

We should migrate away from report_fatal_error as it has been "soft" deprecated in llvm/include/llvm/Support/ErrorHandling.h:

/// @deprecated Use reportFatalInternalError() or reportFatalUsageError()
/// instead.
[[noreturn]] void report_fatal_error(const char *reason,
                                     bool gen_crash_diag = true);

and in llvm/include/llvm/Support/Error.h:

/// @deprecated Use reportFatalInternalError() or reportFatalUsageError()
/// instead.
[[noreturn]] void report_fatal_error(Error Err, bool gen_crash_diag = true);

Once we are done, we should remove the bits to disable -Wno-documentation-deprecated-sync. (#138909)