Make it explicit that this piece of code is only meant to do somethin…

…g for windows platforms

SConstruct

@@ -345,9 +345,10 @@ def kremlin_emitter(target, source, env):
 def add_kremlin(env):
   # In order to succeed, the Kremlin builder needs an extra directory in the
   # PATH on Windows so that the DLL can be properly found.
-  gmp_dll = FindFile('libgmp-10.dll', os.environ['PATH'].split(';'))
-  if gmp_dll != None:
-    env.PrependENVPath('PATH', os.path.dirname(str(gmp_dll)))
+  if sys.platform == 'win32':
+    gmp_dll = FindFile('libgmp-10.dll', os.environ['PATH'].split(';'))
+    if gmp_dll != None:
+      env.PrependENVPath('PATH', os.path.dirname(str(gmp_dll)))
   env['KREMLIN_FLAGS'] = '-warn-error +1..4 -warn-error @4 -skip-compilation -add-include \\"DafnyLib.h\\" -cc msvc'
   kremlin = Builder(action='cd ${TARGET.dir} && ${KREMLIN.abspath} $KREMLIN_FLAGS ${SOURCE.file} $KREMLIN_USER_ARGS',
                            suffix = '.c',