[clang] [driver] Remove obsolete unistd.h include

[tbaeder]

Summary

This was needed for a call to getuid(), but that call is gone these days, so remove the include as well.

[tbaeder]

Pushed as b86e7ae66cb988dda33445c29fa64f93e7ca9c3c

clang/lib/Driver/ToolChains/Clang.cpp

 #include "llvm/Support/Compression.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/TargetParser.h"
 #include "llvm/Support/YAMLParser.h"
 
-#ifdef LLVM_ON_UNIX
-#include <unistd.h> // For getuid().
-#endif
-
 using namespace clang::driver;
 using namespace clang::driver::tools;
 using namespace clang;
 using namespace llvm::opt;
 
 static void CheckPreprocessingOptions(const Driver &D, const ArgList &Args) {
   if (Arg *A =
           Args.getLastArg(clang::driver::options::OPT_C, options::OPT_CC)) {