fix documentation building

An earlier patch added --disable-docs, but went too far, making it
impossible to build the docs.

It turns out that Automake seemingly has a bug preventing the
conditional build of an info file.  So, this patch works around the
bug by putting the info_TEXINFOS rule into a new doc/Makefile.am.

Tested by building with and without --disable-docs and looking for the
existence of doc/libffi.info.

Makefile.am

@@ -5,6 +5,14 @@ AUTOMAKE_OPTIONS = foreign subdir-objects
 ACLOCAL_AMFLAGS = -I m4
 
 SUBDIRS = include testsuite man
+if BUILD_DOCS
+## This hack is needed because it doesn't seem possible to make a
+## conditional info_TEXINFOS in Automake.  At least Automake 1.14
+## either gives errors -- if this attempted in the most
+## straightforward way -- or simply unconditionally tries to build the
+## info file.
+SUBDIRS += doc
+endif
 
 EXTRA_DIST = LICENSE ChangeLog.v1 ChangeLog.libgcj			\
 	ChangeLog.libffi ChangeLog.libffi-3.1				\
@@ -16,11 +24,6 @@ EXTRA_DIST = LICENSE ChangeLog.v1 ChangeLog.libgcj			\
 	libtool-ldflags
 
 
-info_TEXINFOS =
-if BUILD_DOCS
-#info_TEXINFOS += doc/libffi.texi
-endif
-
 ## ################################################################
 
 ##

configure.ac

@@ -380,6 +380,6 @@ test -d src/$TARGETDIR || mkdir src/$TARGETDIR
 
 AC_CONFIG_LINKS(include/ffitarget.h:src/$TARGETDIR/ffitarget.h)
 
-AC_CONFIG_FILES(include/Makefile include/ffi.h Makefile testsuite/Makefile man/Makefile libffi.pc)
+AC_CONFIG_FILES(include/Makefile include/ffi.h Makefile testsuite/Makefile man/Makefile doc/Makefile libffi.pc)
 
 AC_OUTPUT

doc/Makefile.am

@@ -0,0 +1,3 @@
+## Process this with automake to create Makefile.in
+
+info_TEXINFOS = libffi.texi