I'm configuring like this:

    env CC="i686-apple-darwin10-gcc-4.2.1 -mmacosx-version-min=10.5"
./configure --host=i686-apple-darwin --build=i686-apple-darwin --with-ns

It all compiles ok until it gets to macfont.m:

i686-apple-darwin10-gcc-4.2.1 -mmacosx-version-min=10.5  -std=gnu99 -c
-Demacs  -I. -I/Users/david/src/emacs-dev/emacs-bzr/build-2013-09-20/src
-I../lib
-I/Users/david/src/emacs-dev/emacs-bzr/build-2013-09-20/src/../lib
  -I/usr/include/libxml2          -MMD -MF deps/macfont.d -MP     -g3
-O2   macfont.m
macfont.m: In function 'macfont_draw':
macfont.m:2712: error: incompatible type for argument 2 of
'CGContextFillRect'
make[1]: *** [macfont.o] Error 1
make: *** [src] Error 2

On further examination, I found this: http://cocoadev.com/CGRect
which says that you need NSRectToCGRect() on 32 bit Mac OS X platforms
(which explains only the 32 bit compile is failing). Luckily there is
CGRectMake which analagous to NSMakeRect:

https://developer.apple.com/library/mac/documentation/GraphicsImaging/Reference/CGGeometry/Reference/reference.html#//apple_ref/doc/uid/TP30000955-CH1g-F17161

The following patch fixes the issue:

=== modified file 'src/macfont.m'
--- src/macfont.m	2013-09-15 19:36:20 +0000
+++ src/macfont.m	2013-10-02 01:32:30 +0000
@@ -2708,7 +2708,7 @@
     {
       CG_SET_FILL_COLOR_WITH_GC_BACKGROUND (context, s);
       CGContextFillRect (context,
-			 NSMakeRect (x, y,
+			 CGRectMake (x, y,
                                      s->width, FONT_HEIGHT (s->font)));
     }