scons: Bump the compiler version to gcc 4.6 and clang 3.0

This patch bumps the supported version of gcc from 4.4 to 4.6, and
clang from 2.9 to 3.0. This enables, amongst other things, range-based
for loops, lambda expressions, etc. The STL implementation shipping
with 4.6 also has a full functional implementation of unique_ptr and
shared_ptr.

src/SConscript

@@ -925,10 +925,8 @@ def makeEnv(env, label, objsfx, strip = False, **kwargs):
         # warnings about uninitialized variables and missing field
         # initializers.
         swig_env.Append(CCFLAGS=['-Wno-uninitialized',
-                                 '-Wno-missing-field-initializers'])
-
-        if compareVersions(env['GCC_VERSION'], '4.6') >= 0:
-            swig_env.Append(CCFLAGS='-Wno-unused-but-set-variable')
+                                 '-Wno-missing-field-initializers',
+                                 '-Wno-unused-but-set-variable'])
 
         # If gcc supports it, also warn for deletion of derived
         # classes with non-virtual desctructors. For gcc >= 4.7 we