Fix Architecture test to work with Xcode 4

ppc tools are no longer available in the Xcode 4 installation.
Eliminate the use of the hard-coded 'ppc' in the test when
running on Snow Leopard or later.

Tests/Architecture/CMakeLists.txt

@@ -1,6 +1,14 @@
 cmake_minimum_required(VERSION 2.8)
 project(Architecture C)
 
+set(archs i386 ppc)
+
+if(NOT "${DARWIN_MAJOR_VERSION}.${DARWIN_MINOR_VERSION}" VERSION_LESS 10.0)
+  # Snow Leopard or later, use modern architectures as defaults
+  # Arch 'ppc' no longer works: tools no longer available starting with Xcode 4
+  set(archs i386 x86_64)
+endif()
+
 add_library(foo foo.c)
 if(CMAKE_OSX_ARCHITECTURES)
   get_property(archs TARGET foo PROPERTY OSX_ARCHITECTURES)
@@ -11,11 +19,26 @@ if(CMAKE_OSX_ARCHITECTURES)
       )
   endif()
 endif()
-set_property(TARGET foo PROPERTY OSX_ARCHITECTURES i386)
-set_property(TARGET foo PROPERTY OSX_ARCHITECTURES_DEBUG ppc)
+
+list(LENGTH archs archs_len)
+if(archs_len GREATER 1)
+  list(GET archs 0 arch0)
+  list(GET archs 1 arch1)
+else()
+  set(arch0 ${archs})
+  set(arch1 ${archs})
+endif()
+
+message("archs='${archs}'")
+message("arch0='${arch0}'")
+message("arch1='${arch1}'")
+
+set_property(TARGET foo PROPERTY OSX_ARCHITECTURES ${arch0})
+set_property(TARGET foo PROPERTY OSX_ARCHITECTURES_DEBUG ${arch1})
 
 add_executable(bar bar.c)
 target_link_libraries(bar foo)
+
 set_property(TARGET bar PROPERTY OUTPUT_NAME Architecture)
-set_property(TARGET bar PROPERTY OSX_ARCHITECTURES ppc)
-set_property(TARGET bar PROPERTY OSX_ARCHITECTURES_DEBUG i386)
+set_property(TARGET bar PROPERTY OSX_ARCHITECTURES ${arch1})
+set_property(TARGET bar PROPERTY OSX_ARCHITECTURES_DEBUG ${arch0})