diff -r c42575f2cde8 indra/cmake/Variables.cmake
--- a/indra/cmake/Variables.cmake	Sun Oct 16 09:17:27 2011 -0700
+++ b/indra/cmake/Variables.cmake	Tue Oct 18 00:00:36 2011 -0700
@@ -98,33 +98,51 @@
 
 if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   set(DARWIN 1)
-  
-  # To support a different SDK update these Xcode settings:
-  set(CMAKE_OSX_DEPLOYMENT_TARGET 10.5)
-  set(CMAKE_OSX_SYSROOT /Developer/SDKs/MacOSX10.5.sdk)
-  set(CMAKE_XCODE_ATTRIBUTE_GCC_VERSION "4.0")
+
+  # Get the version of Xcode currently installed
+  execute_process(COMMAND "${CMAKE_BUILD_TOOL}" -version COMMAND awk "/Xcode/ {print $NF}"
+                  OUTPUT_VARIABLE XCODE_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+  if("${XCODE_VERSION}" VERSION_EQUAL "4.2"
+  OR "${XCODE_VERSION}" VERSION_GREATER "4.2")
+    # Xcode 4.2 ships with SDKs for Mac OS X 10.6 and 10.7
+    # Compile using LLVM-GCC 4.2
+    set(CMAKE_OSX_DEPLOYMENT_TARGET 10.6)
+    set(CMAKE_OSX_SYSROOT /Developer/SDKs/MacOSX10.6.sdk)
+    set(CMAKE_XCODE_ATTRIBUTE_GCC_VERSION "com.apple.compilers.llvmgcc42")
+
+  elseif("${XCODE_VERSION}" VERSION_EQUAL "4.0"
+      OR "${XCODE_VERSION}" VERSION_GREATER "4.0")
+    message(FATAL_ERROR "Xcode 4.0-4.1 are not supported.")
+
+  elseif("${XCODE_VERSION}" VERSION_EQUAL "3.2"
+      OR "${XCODE_VERSION}" VERSION_GREATER "3.2")
+    # Xcode 3.2 ships with SDKs for Mac OS X 10.5 and 10.6
+    # Compile using GCC 4.0
+    set(CMAKE_OSX_DEPLOYMENT_TARGET 10.5)
+    set(CMAKE_OSX_SYSROOT /Developer/SDKs/MacOSX10.5.sdk)
+    set(CMAKE_XCODE_ATTRIBUTE_GCC_VERSION "4.0")
+
+  else ()
+    message(FATAL_ERROR "Xcode older than 3.2 not supported")
+  endif ()
+
+  # Debug information format stays the same
   set(CMAKE_XCODE_ATTRIBUTE_DEBUG_INFORMATION_FORMAT dwarf-with-dsym)
 
-  # NOTE: To attempt an i386/PPC Universal build, add this on the configure line:
-  # -DCMAKE_OSX_ARCHITECTURES:STRING='i386;ppc'
-  # Build only for i386 by default, system default on MacOSX 10.6 is x86_64
-  if (NOT CMAKE_OSX_ARCHITECTURES)
-    set(CMAKE_OSX_ARCHITECTURES i386)
-  endif (NOT CMAKE_OSX_ARCHITECTURES)
+  ## We currently support only 32-bit i386 builds, so use these:
+  set(CMAKE_OSX_ARCHITECTURES i386)
+  set(ARCH i386)
+  set(WORD_SIZE 32)
 
-  if (CMAKE_OSX_ARCHITECTURES MATCHES "i386" AND CMAKE_OSX_ARCHITECTURES MATCHES "ppc")
-    set(ARCH universal)
-  else (CMAKE_OSX_ARCHITECTURES MATCHES "i386" AND CMAKE_OSX_ARCHITECTURES MATCHES "ppc")
-    if (${CMAKE_SYSTEM_PROCESSOR} MATCHES "ppc")
-      set(ARCH ppc)
-    else (${CMAKE_SYSTEM_PROCESSOR} MATCHES "ppc")
-      set(ARCH i386)
-    endif (${CMAKE_SYSTEM_PROCESSOR} MATCHES "ppc")
-  endif (CMAKE_OSX_ARCHITECTURES MATCHES "i386" AND CMAKE_OSX_ARCHITECTURES MATCHES "ppc")
+  ## But if you want to compile for mixed 32/64 bit, try these:
+  # set(CMAKE_OSX_ARCHITECTURES i386;x86_64)
+  # set(ARCH universal)
+  # set(WORD_SIZE 64)
 
+  # Finally, set up the build output directories
   set(LL_ARCH ${ARCH}_darwin)
   set(LL_ARCH_DIR universal-darwin)
-  set(WORD_SIZE 32)
 endif (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
 
 # Default deploy grid