Modify OS X universal binary creation process to give the user more control over the 32-bit fork (necessary for building universal binaries with libjpeg v7/v8b emulation, for instance)


git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@281 632fc199-4ca6-4c93-a231-07263d6284db
diff --git a/BUILDING.txt b/BUILDING.txt
index 95b2a65..f99babe 100644
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -530,13 +530,15 @@
   Create Macintosh package/disk image.  This requires the PackageMaker
   application, which must be installed in /Developer/Applications/Utilities.
 
-make udmg
+make udmg [BUILDDIR32={32-bit build directory}]
 
   On 64-bit OS X systems, this creates a version of the Macintosh package and
-  disk image which contains universal i386/x86-64 binaries.  The 32-bit fork of
-  these binaries is backward compatible with OS X 10.4 and later.  The 64-bit
-  fork can be made backward compatible as well by using the instructions in
-  the "Build Recipes" section.  OS X 10.4 compatibility SDK required.
+  disk image which contains universal i386/x86-64 binaries.  You should first
+  configure a 32-bit out-of-tree build of libjpeg-turbo, then configure a
+  64-bit out-of-tree build, then run 'make udmg' from the 64-bit build
+  directory.  The build system will look for the 32-bit build under
+  {source_directory}/osxx86 by default, but you can override this by setting
+  the BUILDDIR32 variable on the make command line as shown above.
 
 make cygwinpkg