Fix for issue #7724: make it possible to build using

the OSX 10.4u SDK on MacOSX 10.6 by honoring the specified
SDK when looking for files.

unixccompiler.py

@@ -15,7 +15,7 @@ the "typical" Unix-style command-line C compiler:
 
 __revision__ = "$Id$"
 
-import os, sys
+import os, sys, re
 from types import StringType, NoneType
 
 from distutils import sysconfig
@@ -305,10 +305,29 @@ class UnixCCompiler(CCompiler):
         dylib_f = self.library_filename(lib, lib_type='dylib')
         static_f = self.library_filename(lib, lib_type='static')
 
+        if sys.platform == 'darwin':
+            # On OSX users can specify an alternate SDK using
+            # '-isysroot', calculate the SDK root if it is specified
+            # (and use it further on)
+            cflags = sysconfig.get_config_var('CFLAGS')
+            m = re.search(r'-isysroot\s+(\S+)', cflags)
+            if m is None:
+                sysroot = '/'
+            else:
+                sysroot = m.group(1)
+
+
+
         for dir in dirs:
             shared = os.path.join(dir, shared_f)
             dylib = os.path.join(dir, dylib_f)
             static = os.path.join(dir, static_f)
+
+            if sys.platform == 'darwin' and (dir.startswith('/System/') or dir.startswith('/usr/')):
+                shared = os.path.join(sysroot, dir[1:], shared_f)
+                dylib = os.path.join(sysroot, dir[1:], dylib_f)
+                static = os.path.join(sysroot, dir[1:], static_f)
+
             # We're second-guessing the linker here, with not much hard
             # data to go on: GCC seems to prefer the shared library, so I'm
             # assuming that *all* Unix C compilers do.  And of course I'm