Fix deprecated use of 0/NULL in gloo/cuda_allreduce_ring_chunked.h + 3

Summary:
`nullptr` is typesafe. `0` and `NULL` are not. In the future, only `nullptr` will be allowed.

This diff helps us embrace the future _now_ in service of enabling `-Wzero-as-null-pointer-constant`.

Reviewed By: meyering

Differential Revision: D54163047

fbshipit-source-id: 6f44e83af686111d6f47d51b81a3108ceb01b31e

Author: r-barnes

gloo/cuda_allreduce_ring_chunked.h

@@ -37,12 +37,12 @@ class CudaAllreduceRingChunked : public Algorithm {
   template <typename U = W>
   void init(
     typename std::enable_if<std::is_same<U, CudaHostWorkspace<T> >::value,
-    typename U::Pointer>::type* = 0);
+    typename U::Pointer>::type* = nullptr);
 
   template <typename U = W>
   void init(
     typename std::enable_if<std::is_same<U, CudaDeviceWorkspace<T> >::value,
-    typename U::Pointer>::type* = 0);
+    typename U::Pointer>::type* = nullptr);
 
   std::vector<CudaDevicePointer<T> > devicePtrs_;
   std::vector<CudaStream> streams_;

gloo/transport/tcp/tls/context.cc

@@ -56,8 +56,8 @@ SSL_CTX *Context::create_ssl_ctx(const char *pkey, const char *cert,
     //    SSL_load_error_strings();
     //    SSL_library_init();
     _glootls::OPENSSL_init_ssl(
-        OPENSSL_INIT_LOAD_SSL_STRINGS | OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
-    _glootls::OPENSSL_init_ssl(0, NULL);
+        OPENSSL_INIT_LOAD_SSL_STRINGS | OPENSSL_INIT_LOAD_CRYPTO_STRINGS, nullptr);
+    _glootls::OPENSSL_init_ssl(0, nullptr);
   });
   SSL_CTX *ssl_ctx = _glootls::SSL_CTX_new(_glootls::TLS_method());
   GLOO_ENFORCE(ssl_ctx != nullptr, getSSLErrorMessage());