Get alloca boilerplate right.

src/Hist.cc

@@ -10,6 +10,7 @@
  * Illinois Open Source License; see the file LICENSE.partiview for details.
  */
 
+#ifndef __GNUC__
 # if HAVE_ALLOCA_H
 #  include <alloca.h>
 # else
@@ -21,7 +22,7 @@ extern char *alloca ();
 #   endif
 #  endif
 # endif
-
+#endif
 
 #include "FL/Fl.H"
 #include "FL/Fl_Browser.H"