Later versions of autoconf (specifically, the one shipped with Xcode 4.3) default to building x86-64, so it is necessary to override the host_alias to get a 32-bit build.

git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@845 632fc199-4ca6-4c93-a231-07263d6284db

BUILDING.txt

@@ -203,7 +203,7 @@ installed.
 
 Add
 
-  CFLAGS='-O3 -m32' LDFLAGS=-m32
+  --host i686-apple-darwin CFLAGS='-O3 -m32' LDFLAGS=-m32
 
 to the configure command line.
 
@@ -228,7 +228,8 @@ MacPorts, must be installed.
 
 Add
 
-  CFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
+  --host i686-apple-darwin \
+    CFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
     -mmacosx-version-min=10.4 -O3 -m32' \
     LDFLAGS='-isysroot /Developer/SDKs/MacOSX10.4u.sdk \
     -mmacosx-version-min=10.4 -m32'