add Environment.execute(); implement first version of Program builder

lib/rscons/builders/cc.rb

@@ -7,7 +7,7 @@ module Rscons
       'OBJSUFFIX' => '.o',
     }
 
-    def run(env, sources)
+    def run(env, target, sources)
     end
   end
 end

lib/rscons/builders/program.rb

@@ -5,10 +5,20 @@ module Rscons
       'OBJSUFFIX' => '.o',
       'LIBSUFFIX' => '.a',
       'LDFLAGS' => [],
+      'LIBPATHS' => [],
       'LIBS' => [],
     }
 
-    def run(env, sources)
+    def run(env, target, sources)
+      command = [
+        env['LD'] || env['CC'],
+        '-o', target,
+        *env['LDFLAGS'],
+        *sources,
+        *env['LIBPATHS'].map {|lp| "-L#{lp}"},
+        *env['LIBS'].map {|lib| "-l#{lib}"}
+      ]
+      env.execute("LINK #{target}", command)
     end
   end
 end