diff -r e4016b6abbb2 tools/build/v2/tools/clang-darwin.jam
--- a/tools/build/v2/tools/clang-darwin.jam	Mon Mar 14 12:31:12 2011 +0100
+++ b/tools/build/v2/tools/clang-darwin.jam	Mon Mar 14 13:09:27 2011 +0100
@@ -34,6 +34,10 @@
           <warnings>off <warnings>all <warnings>on
           <architecture>x86/<address-model>32
           <architecture>x86/<address-model>64
+          <architecture>x86/<instruction-set>
+	  <architecture>arm/<address-model>32
+     	  <architecture>arm/<address-model>64
+     	  <architecture>arm/<instruction-set>
         ;
         
 if [ MATCH (--debug-configuration) : [ modules.peek : ARGV ] ]
@@ -68,8 +72,139 @@
 
     gcc.init-link-flags clang-darwin darwin $(condition) ;
 
+    # - Initialize the SDKs available in the root for this tool.
+    local sdks = [ init-available-sdk-versions $(condition) : $(root) ] ;
 }
 
+# Add and set options for a discovered SDK version.
+local rule init-sdk ( condition * : root ? : version + : version-feature ? )
+{
+    local rule version-to-feature ( version + )
+    {
+        switch $(version[1])
+        {
+            case iphone* :
+            {
+                return $(version[1])-$(version[2-]:J=.) ;
+            }
+            case mac* :
+            {
+                return $(version[2-]:J=.) ;
+            }
+            case * :
+            {
+                return $(version:J=.) ;
+            }
+        }
+    }
+    
+    if $(version-feature)
+    {
+        if $(.debug-configuration)
+        {
+            ECHO notice: available sdk for $(condition)/<macosx-version>$(version-feature) at $(sdk) ;
+        }
+        
+        # Add the version to the features for specifying them.
+        if ! $(version-feature) in [ feature.values macosx-version ]
+        {
+            feature.extend macosx-version : $(version-feature) ;
+        }
+        if ! $(version-feature) in [ feature.values macosx-version-min ]
+        {
+            feature.extend macosx-version-min : $(version-feature) ;
+        }
+        
+        # Set the flags the version needs to compile with, first
+        # generic options.
+        flags darwin.compile OPTIONS $(condition)/<macosx-version>$(version-feature)
+            : -isysroot $(sdk) ;
+        flags darwin.link OPTIONS $(condition)/<macosx-version>$(version-feature)
+            : -isysroot $(sdk) ;
+        
+        # Then device variation options.
+        switch $(version[1])
+        {
+            case iphone* :
+            {
+                flags darwin.compile OPTIONS <macosx-version-min>$(version-feature)
+                    : -miphoneos-version-min=$(version[2-]:J=.) ;
+                flags darwin.link OPTIONS <macosx-version-min>$(version-feature)
+                    : -miphoneos-version-min=$(version[2-]:J=.) ;
+            }
+            
+            case mac* :
+            {
+                flags darwin.compile OPTIONS <macosx-version-min>$(version-feature)
+                    : -mmacosx-version-min=$(version[2-]:J=.) ;
+                flags darwin.link OPTIONS <macosx-version-min>$(version-feature)
+                    : -mmacosx-version-min=$(version[2-]:J=.) ;
+            }
+        }
+        
+        return $(version-feature) ;
+    }
+    else if $(version[4])
+    {
+        # We have a patch version of an SDK. We want to set up
+        # both the specific patch version, and the minor version.
+        # So we recurse to set up the minor version. Plus the minor version.
+        return
+            [ init-sdk $(condition) : $(root)
+                : $(version[1-3]) : [ version-to-feature $(version[1-3]) ] ]
+            [ init-sdk $(condition) : $(root)
+                : $(version) : [ version-to-feature $(version) ] ] ;
+    }
+    else
+    {
+        # Yes, this is intentionally recursive.
+        return
+            [ init-sdk $(condition) : $(root)
+                : $(version) : [ version-to-feature $(version) ] ] ;
+    }
+}
+
+# Determine the MacOSX SDK versions installed and their locations.
+local rule init-available-sdk-versions ( condition * : root ? )
+{
+    root ?= /Developer ;
+    local sdks-root = $(root)/SDKs ;
+    local sdks = [ GLOB $(sdks-root) : MacOSX*.sdk iPhoneOS*.sdk iPhoneSimulator*.sdk ] ;
+    local result ;
+    for local sdk in $(sdks)
+    {
+        local sdk-match = [ MATCH ([^0-9]+)([0-9]+)[.]([0-9x]+)[.]?([0-9x]+)? : $(sdk:D=) ] ;
+        local sdk-platform = $(sdk-match[1]:L) ;
+        local sdk-version = $(sdk-match[2-]) ;
+        if $(sdk-version)
+        {
+            switch $(sdk-platform)
+            {
+                case macosx :
+                {
+                    sdk-version = mac $(sdk-version) ;
+                }
+                case iphoneos :
+                {
+                    sdk-version = iphone $(sdk-version) ;
+                }
+                case iphonesimulator :
+                {
+                    sdk-version = iphonesim $(sdk-version) ;
+                }
+                case * :
+                {
+                    sdk-version = $(sdk-version:J=-) ;
+                }
+            }
+            result += [ init-sdk $(condition) : $(sdk) : $(sdk-version) ] ;
+        }
+    }
+    return $(result) ;
+}
+
+
+
 SPACE = " " ;
 
 flags clang-darwin.compile OPTIONS <cflags> ;