Explain why we are making gcc 3.3 work

changes/portability_01_haiku

@@ -6,6 +6,9 @@
       analysis by Martin Hebnes Pedersen.
     - Preprocessor directives should not be put inside the arguments
       of a macro. This would break compilation with GCC releases prior
-      to version 3.3. Bugfix on 0.2.3.3-alpha, fixes the other part of
-      bug 4727. Patch and analysis by Martin Hebnes Pedersen.
+      to version 3.3. We would never recommend such an old GCC
+      version, but it is apparently required for binary compatibility
+      on some platforms (namely, certain builds of Haiku). Bugfix on
+      0.2.3.3-alpha, fixes the other part of bug 4727. Patch and
+      analysis by Martin Hebnes Pedersen.