Rearrange some configure.in comments for better readability.

Commit configure and pg_config.h.in, missed in last configure.in
update.

configure.in

@@ -1,5 +1,5 @@
 dnl Process this file with autoconf to produce a configure script.
-dnl $PostgreSQL: pgsql/configure.in,v 1.463 2006/04/29 16:34:41 momjian Exp $
+dnl $PostgreSQL: pgsql/configure.in,v 1.464 2006/04/29 20:47:29 tgl Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -248,19 +248,20 @@ else
   fi
 fi
 
-# The Intel compiler on Linux supports most gcc options, but not
-# all of them, so only add these options if we are really using
-# gcc.
+# Some versions of GCC support some additional useful warning flags.
+# Check whether they are supported, and add them to CFLAGS if so.
 
 if test "$GCC" = yes; then
+
+# ICC pretends to be GCC but it's lying; it doesn't support these options.
+# So we have to check if "GCC" is really ICC.
 AC_TRY_COMPILE([], [@%:@ifndef __INTEL_COMPILER
 choke me
 @%:@endif], [ICC=[yes]], [ICC=[no]])
+
   if test "$ICC" = no; then
     CFLAGS="$CFLAGS -Wall -Wmissing-prototypes -Wpointer-arith -Winline"
 
-    # Some versions of GCC support some additional useful warning flags.
-    # Check whether they are supported, and add them to CFLAGS if so.
     PGAC_PROG_CC_CFLAGS_OPT([-Wdeclaration-after-statement])
     PGAC_PROG_CC_CFLAGS_OPT([-Wendif-labels])
   else