Add missing namespace to PPCLinux.cpp

[glandium]

Summary

This fixes a build failure with MSVC introduced in
https://reviews.llvm.org/D112906

[nemanjai]

LGTM.

clang/lib/Driver/ToolChains/PPCLinux.cpp

 //===-- PPCLinux.cpp - PowerPC ToolChain Implementations --------*- C++ -*-===//
 //
 // 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 "PPCLinux.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 
+using namespace clang::driver;
 using namespace clang::driver::toolchains;
 using namespace llvm::opt;
 using namespace llvm::sys;
 
 // Glibc older than 2.32 doesn't fully support IEEE float128. Here we check
 // glibc version by looking at dynamic linker name.
 static bool GlibcSupportsFloat128(const std::string &Linker) {
   llvm::SmallVector<char, 16> Path;