[glom] Build: Disable use of yelp if --disable-documentation was used.

[Murray Cumming <murrayc src gnome org>]

commit 6de5b81ca85f597b47b15a28054a94f03b3de45a
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Sep 8 21:20:56 2015 +0200

    Build: Disable use of yelp if --disable-documentation was used.
    
    Until now it was just used to disable generation/installation of
    the libglom API reference documentation.
    
    This should apparently be useful on MacOS:
    https://trac.macports.org/ticket/44616

 Makefile.am  |    5 ++++-
 configure.ac |    4 ++--
 2 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 386bb5b..6763dc8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -40,8 +40,11 @@ else
 doc_subdirs =
 endif
 
-# TODO: Allow this to be disabled, by letting YELP_HELP_INIT fail nicely as it could with GNOME_DOC_INIT?
+if ENABLE_DOCUMENTATION
+yelp_doc_subdirs = docs/user-guide
+else
 yelp_doc_subdirs = docs/user-guide
+endif
 
 SUBDIRS = po $(doc_subdirs) $(yelp_doc_subdirs)
 
diff --git a/configure.ac b/configure.ac
index 5b80b3d..d590041 100644
--- a/configure.ac
+++ b/configure.ac
@@ -313,8 +313,8 @@ AS_IF([test "x$glom_host_win32" != xyes && test "x$glom_enable_client_only" != x
 AC_DEFINE_UNQUOTED([MYSQL_UTILS_PATH], ["$MYSQL_UTILS_PATH"],
                    [Define to the location of the MySQL utilities.])
 
-
-YELP_HELP_INIT
+AS_IF([test "x$ENABLE_DOCUMENTATION" != xno],
+  [YELP_HELP_INIT])
 
 MM_ARG_ENABLE_DOCUMENTATION
 MM_ARG_WITH_TAGFILE_DOC([libstdc++.tag], [mm-common-libstdc++])