update examples in manual to use PKG_CHECK_MODULES

* doc/ref/autoconf.texi (Using Autoconf Macros): Switch example to use
  PKG_CHECK_MODULES.
* doc/ref/libguile-linking.texi (A Sample Guile Main Program): Likewise,
  and change from configure.in to configure.ac, and recommend
  autoreconf.

doc/ref/autoconf.texi

@@ -1,6 +1,6 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
-@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2009
+@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2009, 2011
 @c   Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
@@ -97,25 +97,25 @@ to instantiate macros at top-level.
 
 We now include two examples, one simple and one complicated.
 
-The first example is for a package that uses libguile, and thus needs to know
+The first example is for a package that uses libguile, and thus needs to
-how to compile and link against it.  So we use @code{GUILE_FLAGS} to set the
+know how to compile and link against it.  So we use
-vars @code{GUILE_CFLAGS} and @code{GUILE_LDFLAGS}, which are automatically
+@code{PKG_CHECK_MODULES} to set the vars @code{GUILE_CFLAGS} and
-substituted in the Makefile.
+@code{GUILE_LIBS}, which are automatically substituted in the Makefile.
 
 @example
 In configure.ac:
 
-  GUILE_FLAGS
+  PKG_CHECK_MODULES([GUILE], [guile-@value{EFFECTIVE-VERSION}])
 
 In Makefile.in:
 
   GUILE_CFLAGS  = @@GUILE_CFLAGS@@
-  GUILE_LDFLAGS = @@GUILE_LDFLAGS@@
+  GUILE_LIBS = @@GUILE_LIBS@@
 
   myprog.o: myprog.c
           $(CC) -o $@ $(GUILE_CFLAGS) $<
   myprog: myprog.o
-          $(CC) -o $@ $< $(GUILE_LDFLAGS)
+          $(CC) -o $@ $< $(GUILE_LIBS)
 @end example
 
 The second example is for a package of Guile Scheme modules that uses an

doc/ref/libguile-linking.texi

@@ -128,13 +128,11 @@ simple-guile.o: simple-guile.c
 If you are using the GNU Autoconf package to make your application more
 portable, Autoconf will settle many of the details in the Makefile above
 automatically, making it much simpler and more portable; we recommend
-using Autoconf with Guile.  Guile also provides the @code{GUILE_FLAGS}
+using Autoconf with Guile.  Here is a @file{configure.ac} file for
-macro for autoconf that performs all necessary checks.  Here is a
+@code{simple-guile} that uses the standard @code{PKG_CHECK_MODULES}
-@file{configure.in} file for @code{simple-guile} that uses this macro.
+macro to check for Guile.  Autoconf will process this file into a
-Autoconf can use this file as a template to generate a @code{configure}
+@code{configure} script.  We recommend invoking Autoconf via the
-script.  In order for Autoconf to find the @code{GUILE_FLAGS} macro, you
+@code{autoreconf} utility.
-will need to run @code{aclocal} first (@pxref{Invoking aclocal,,,
-automake, GNU Automake}).
 
 @example
 AC_INIT(simple-guile.c)
@@ -143,19 +141,21 @@ AC_INIT(simple-guile.c)
 AC_PROG_CC
 
 # Check for Guile
-GUILE_FLAGS
+PKG_CHECK_MODULES([GUILE], [guile-@value{EFFECTIVE-VERSION}])
 
 # Generate a Makefile, based on the results.
 AC_OUTPUT(Makefile)
 @end example
 
+Run @code{autoreconf -vif} to generate @code{configure}.
+
 Here is a @code{Makefile.in} template, from which the @code{configure}
 script produces a Makefile customized for the host system:
 @example
 # The configure script fills in these values.
 CC=@@CC@@
 CFLAGS=@@GUILE_CFLAGS@@
-LIBS=@@GUILE_LDFLAGS@@
+LIBS=@@GUILE_LIBS@@
 
 simple-guile: simple-guile.o
         $@{CC@} simple-guile.o $@{LIBS@} -o simple-guile
@@ -164,23 +164,28 @@ simple-guile.o: simple-guile.c
 @end example
 
 The developer should use Autoconf to generate the @file{configure}
-script from the @file{configure.in} template, and distribute
+script from the @file{configure.ac} template, and distribute
 @file{configure} with the application.  Here's how a user might go about
 building the application:
 
 @example
 $ ls
-Makefile.in     configure*      configure.in    simple-guile.c
+Makefile.in     configure*      configure.ac    simple-guile.c
 $ ./configure
-creating cache ./config.cache
+checking for gcc... ccache gcc
-checking for gcc... (cached) gcc
+checking whether the C compiler works... yes
-checking whether the C compiler (gcc  ) works... yes
+checking for C compiler default output file name... a.out
-checking whether the C compiler (gcc  ) is a cross-compiler... no
+checking for suffix of executables... 
-checking whether we are using GNU C... (cached) yes
+checking whether we are cross compiling... no
-checking whether gcc accepts -g... (cached) yes
+checking for suffix of object files... o
-checking for Guile... yes
+checking whether we are using the GNU C compiler... yes
-creating ./config.status
+checking whether ccache gcc accepts -g... yes
-creating Makefile
+checking for ccache gcc option to accept ISO C89... none needed
+checking for pkg-config... /usr/bin/pkg-config
+checking pkg-config is at least version 0.9.0... yes
+checking for GUILE... yes
+configure: creating ./config.status
+config.status: creating Makefile
 $ make
 [...]
 $ ./simple-guile