title: How to specify a value for a #define with autoconf?
body: <p>I'm trying to build Gnu binutils with behaviour unlocked by defining the macro <code>SYSV386_COMPAT 0</code> to vary the way in which it generates some FPU opcodes. </p>
  
  <p>I can easily go into the header file and set the value manually, but how would I invoke the configure script in order to specify the equivalent of <code>#define SYSV386_COMPAT 0</code> on the command line? I would prefer to specify something on the command line if at all possible (just because the feature is transitive and I don't think I should be hacking the source). Having said that, I have tried to read at least some of the FM but have had no luck with inserting an <code>AC_DEFINE(SYSV386_COMPAT, 0)</code> in either <code>binutils/configure.in</code> or <code>gas/configure.in</code>. </p>