Revert "MDEV-19129: Xcode compatibility update: deprecated vfork -> fork"

This reverts commit 5d6f3ceb.

storage/connect/tabrest.cpp

@@ -112,7 +112,7 @@ int Xcurl(PGLOBAL g, PCSZ Http, PCSZ Uri, PCSZ filename)
 
 	} // endif f
 	
-	pID = fork();
+	pID = vfork();
 	sprintf(fn, "-o%s", filename);
 
 	if (pID == 0) {