man: rework the Makefile.am

Remove GNU make specific constructs and take into consideration that
Solaris man 7 is not the same as Linux man 7.

This commit introduces a dependency of xorg-macros 1.12 (released 4+
years ago) which is used to handle the above man section discrepancies.

Cc: Niveditha Rau <niveditha.rau@oracle.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/configure.ac b/configure.ac
index 320e482..f8adf4f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,6 +29,13 @@
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_AUX_DIR([build-aux])
 
+# Require xorg-macros minimum of 1.12 for XORG_WITH_XSLTPROC
+m4_ifndef([XORG_MACROS_VERSION],
+          [m4_fatal([must install xorg-macros 1.12 or later before running autoconf/autogen])])
+XORG_MACROS_VERSION(1.12)
+XORG_WITH_XSLTPROC
+XORG_MANPAGE_SECTIONS
+
 AM_INIT_AUTOMAKE([1.10 foreign dist-bzip2])
 
 # Enable quiet compiles on automake 1.11.
@@ -378,9 +385,8 @@
 
 # xsltproc for docbook manpages
 AC_ARG_ENABLE([manpages],
-              AS_HELP_STRING([--disable-manpages], [disable manpages @<:@default=enabled@:>@]),
+              AS_HELP_STRING([--enable-manpages], [enable manpages @<:@default=auto@:>@]),
               [MANS=$enableval], [MANS=auto])
-AC_PATH_PROG(XSLTPROC, xsltproc)
 AM_CONDITIONAL([BUILD_MANPAGES], [test "x$XSLTPROC" != "x" -a "x$MANS" != "xno"])
 
 # check for offline man-pages stylesheet