[lldb] Fix build on older FreeBSD

[brooks]

Summary

Commit 392d9eb03af5a1adac66a86939351b22b3e73495 added a dependency on
FPE_FLTIDO which was only defined in FreeBSD main on May 19, 2022 and it
not in all releases. Just define it if it's missing.

[dim]

LGTM, but if such SIGFPE's occur before the FPE_FLTIDO define was introduced, can they ever have value 9?

[emaste]

In D147300#4236033, @dim wrote:

LGTM, but if such SIGFPE's occur before the FPE_FLTIDO define was introduced, can they ever have value 9?

This is essentially a compile-time assertion to make sure we have the correct value for FPE_FLTIDO. If we're building on an older FreeBSD which does not have it defined then we can't check it anyway.

We could run an LLDB built on older FreeBSD on a newer kernel and receive FPE_FLTIDO I imagine.

[DavidSpickett]

Thanks!

lldb/source/Plugins/Process/Utility/FreeBSDSignals.cpp

 //===-- FreeBSDSignals.cpp ------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "FreeBSDSignals.h"
 
 #ifdef __FreeBSD__
 #include <csignal>
 
+#ifndef FPE_FLTIDO
+#define FPE_FLTIDO 9
+#endif
+
 #define ADD_SIGCODE(signal_name, signal_value, code_name, code_value, ...)     \
   static_assert(signal_name == signal_value,                                   \
                 "Value mismatch for signal number " #signal_name);             \
   static_assert(code_name == code_value,                                       \
                 "Value mismatch for signal code " #code_name);                 \
   AddSignalCode(signal_value, code_value, __VA_ARGS__)
 #else
 #define ADD_SIGCODE(signal_name, signal_value, code_name, code_value, ...)     \