the build doesn't actually use the openssl var for anything useful.
it blindly adds it to the -I/-L paths which causes problems when you
cross-compile and when you link (it also adds it to -rpath).  punt
the setting and forget about it.

--- a/SConstruct
+++ b/SConstruct
@@ -354,8 +354,6 @@ else:
     apr_libs = ''
     apu_libs = ''
 
-  env.Append(CPPPATH=['$OPENSSL/include'])
-  env.Append(LIBPATH=['$OPENSSL/lib'])
 
 
 # If build with gssapi, get its information and define SERF_HAVE_GSSAPI
@@ -369,8 +369,9 @@ if sys.platform == 'win32':
 # On some systems, the -R values that APR describes never make it into actual
 # RPATH flags. We'll manually map all directories in LIBPATH into new
 # flags to set RPATH values.
-for d in env['LIBPATH']:
-  env.Append(RPATH=':'+d)
+if env.get('LIBPATH', None):
+  for d in env['LIBPATH']:
+    env.Append(RPATH=':'+d)
 
 # Set up the construction of serf-*.pc
 pkgconfig = env.Textfile('serf-%d.pc' % (MAJOR,),