[libc] Fix typo of namespace in round implementation.

[PaulkaToast]

Summary

Fixed typos in namespace declarations and comments in the files under src/math/round.

libc/src/math/round/round.h

 //===------------------ Implementation header for round -------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SRC_MATH_ROUND_H
 #define LLVM_LIBC_SRC_MATH_ROUND_H
 
-namespace llvm_libc {
+namespace __llvm_libc {
 
 double round(double x);
 
-} // namespace llvm_libc
+} // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_MATH_ROUND_H

libc/src/math/round/round.cpp

 //===---------------------- Implementation of round -----------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "src/math/round/round.h"
 
 #include "src/__support/common.h"
 
-namespace llvm_libc {
+namespace __llvm_libc {
 
 double __round_redirector(double x);
 
 double LLVM_LIBC_ENTRYPOINT(round)(double x) {
   return __round_redirector(x);
 }
 
-} // namespace llvm_libc
+} // namespace __llvm_libc

libc/src/math/round/round_redirector.cpp

 //===----------------  Implementation of round redirector -----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <math.h>
 
-namespace llvm_libc {
+namespace __llvm_libc {
 
 double __round_redirector(double x) {
   return ::round(x);
 }
 
-} // namespace llvm_libc
+} // namespace __llvm_libc