pc_from_ucontext.m4

   if ! $pc_field_found; then
     pc_fields="           eip"  # Haiku (i386)
     pc_fields="$pc_fields rip"  # Haiku (x86_64)
     for pc_field in $pc_fields; do
       if ! $pc_field_found; then
         AC_TRY_COMPILE([#include <signal.h>],
                        [ucontext_t u; return u.uc_mcontext.$pc_field == 0;],
                        AC_DEFINE_UNQUOTED(PC_FROM_UCONTEXT, $pc_field,
                                           How to access the PC from a struct ucontext)
                        AC_MSG_RESULT([$pc_field])
                        pc_field_found=true)
       fi
     done
   fi