change builder VARIABLE_DEFAULTS constant to default_variables() class method

lib/rscons/builders/cc.rb

@@ -1,6 +1,7 @@
 module Rscons
   class CC < Builder
-    VARIABLE_DEFAULTS = {
+    def self.default_variables(env)
+      {
         'CC' => 'gcc',
         'CFLAGS' => [],
         'CPPFLAGS' => [],
@@ -8,6 +9,7 @@ module Rscons
         'CEXTS' => ['.c'],
         'CCCOM' => ['$CC', '-c', '-o', '$TARGET', '$CPPFLAGS', '$CFLAGS', '$SOURCES']
       }
+    end
 
     def self.produces?(env, suffix)
       suffix == env['OBJSUFFIX']

lib/rscons/builders/program.rb

@@ -1,6 +1,7 @@
 module Rscons
   class Program < Builder
-    VARIABLE_DEFAULTS = {
+    def self.default_variables(env)
+      {
         'LD' => nil,
         'OBJSUFFIX' => '.o',
         'LIBSUFFIX' => '.a',
@@ -9,6 +10,7 @@ module Rscons
         'LIBS' => [],
         'LDCOM' => ['$LD', '-o', '$TARGET', '$LDFLAGS', '$SOURCES', '-L$[LIBPATHS]', '-l$[LIBS]']
       }
+    end
 
     def run(env, target, sources)
       sources = [sources] if sources.is_a?(String)

lib/rscons/environment.rb

@@ -25,7 +25,7 @@ module Rscons
 
     def add_builder(builder_class)
       @builders[builder_class.to_s.split(':').last] = builder_class
-      var_defs = builder_class.const_get('VARIABLE_DEFAULTS')
+      var_defs = builder_class.default_variables(self)
       if var_defs
         var_defs.each_pair do |var, val|
           unless @variables.has_key?(var)