Allow building without documentation.

Allows building without documentation even if asciidoc and xmlto are
installed. This eases up working with the build system because doc
generation take quite a while on repeated builds.
Signed-off-by: Mikko Koppanen <mkoppanen@php.net>

acinclude.m4

@@ -65,6 +65,14 @@ dnl # AC_CHECK_DOC_BUILD
 dnl # Check whether to build documentation and install man-pages                 #
 dnl ##############################################################################
 AC_DEFUN([AC_CHECK_DOC_BUILD], [{
+    # Allow user to disable doc build
+    AC_ARG_WITH([documentation], [AS_HELP_STRING([--without-documentation],
+        [disable documentation build even if asciidoc and xmlto are present [default=no]])])
+
+    if test "x$with_documentation" = "xno"; then
+        build_doc="no"
+        install_man="no"
+    else
         # Determine whether or not documentation should be built and installed.
         build_doc="yes"
         install_man="yes"
@@ -85,6 +93,7 @@ AC_DEFUN([AC_CHECK_DOC_BUILD], [{
         if test "x$on_mingw32" = "xyes"; then
             install_man="no"
         fi
+    fi
 
     AC_MSG_CHECKING([whether to build documentation])
     AC_MSG_RESULT([$build_doc])