[ VM / dart:io ] Removed usage of std::make_unique as C++14 is not supported in google3

Change-Id: I615bcb89ef2dec2e745a4d321a13a0a131ba7485
Reviewed-on: https://dart-review.googlesource.com/c/83230
Commit-Queue: Ben Konyi <[email protected]>
Commit-Queue: Siva Annamalai <[email protected]>
Auto-Submit: Ben Konyi <[email protected]>
Reviewed-by: Siva Annamalai <[email protected]>

Author: bkonyi

runtime/bin/security_context_macos.cc

@@ -62,7 +62,7 @@ static SecCertificateRef CreateSecCertificateFromX509(X509* cert) {
   if (length < 0) {
     return 0;
   }
-  auto deb_cert = std::make_unique<unsigned char[]>(length);
+  auto deb_cert = std::unique_ptr<unsigned char[]>(new unsigned char[length]);
   unsigned char* temp = deb_cert.get();
   if (i2d_X509(cert, &temp) != length) {
     return NULL;