Arrange to compile flex output files as inclusions into other files

(usually bison output files), not as standalone files.  This hack
works around flex's insistence on including <stdio.h> before we are
able to include postgres.h; postgres.h will already be read before
the compiler starts to read the flex output file.  Needed for largefile
support on some platforms.

contrib/seg/segparse.y

@@ -179,4 +179,4 @@ int seg_yyerror ( char *msg ) {
   return 0;
 }
 
-
+#include "segscan.c"