scons: Use -Werror MSVC compatibility flags per-directory.

Matching what we already do with autotools builds.

Reviewed-by: Brian Paul <brianp@vmware.com>
diff --git a/src/loader/SConscript b/src/loader/SConscript
index 359fc18..16d1053 100644
--- a/src/loader/SConscript
+++ b/src/loader/SConscript
@@ -2,6 +2,8 @@
 
 env = env.Clone()
 
+env.MSVC2013Compat()
+
 env.Prepend(CPPPATH = [
     '#include'
 ])