[lldb] Fix build on older FreeBSD

Commit 392d9eb added a dependency on
FPE_FLTIDO which was only defined in FreeBSD main on May 19, 2022 and
is not in all supported releases. Just define it if it's missing as we
could use a debugger compiled on an older system to debug a newer one.

Reviewed by: DavidSpickett, emaste, dim

Differential Revision: https://reviews.llvm.org/D147300

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

@@ -11,6 +11,10 @@
 #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);             \