pass extra variables into Environment.execute()

lib/rscons/builders/cc.rb

@@ -23,7 +23,11 @@ module Rscons
           '-o', o_file,
           source
         ]
-        env.execute("CC #{o_file}", command)
+        vars = {
+          'TARGET' => o_file,
+          'SOURCES' => source,
+        }
+        env.execute("CC #{o_file}", command, vars)
         Cache.open.register_build(target, [source])
       end
       o_file

lib/rscons/builders/program.rb

@@ -34,7 +34,11 @@ module Rscons
           *env['LIBPATHS'].map {|lp| "-L#{lp}"},
           *env['LIBS'].map {|lib| "-l#{lib}"}
         ]
-        env.execute("LINK #{target}", command)
+        vars = {
+          'TARGET' => target,
+          'SOURCES' => sources,
+        }
+        env.execute("LINK #{target}", command, vars)
         Cache.open.register_build(target, sources)
       end
       target