Don't use exec if it's not needed

SConstruct

@@ -516,7 +516,7 @@ env.Clean(all, 'TAGS')
 #
 
 for d in installdirs:
-    exec d + ' = os.path.join(env["destdir"], env[d].lstrip("/"))'
+    locals()[d] = os.path.join(env["destdir"], env[d].lstrip("/"))
 installable_subs = Split('data fonts images sounds')
 if os.path.isabs(env["localedirname"]):
     env["localedir"] = env["localedirname"]

src/SConscript

@@ -514,7 +514,7 @@ def WesnothProgram(env, target, source, can_build, **kw):
     else:
         bin = env.Alias(target, [], error_action)
         AlwaysBuild(bin)
-    exec target + " = bin"
+    locals()[target] = bin
     Export(target)
 
 for env in [test_env, client_env, env]: