clang/AMDGPU: Use Support's wrapper around getenv

[arsenm]

Summary

This does some extra stuff for Windows, so might as well
use it just in case.

[yaxunl]

LGTM. Thanks.

[arsenm]

840a793375fec763c2b2781b82b764325635cc7a

clang/lib/Driver/ToolChains/AMDGPU.cpp

 #include "clang/Driver/InputInfo.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileUtilities.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include <system_error>
 
 #define AMDGPU_ARCH_PROGRAM_NAME "amdgpu-arch"
 
 using namespace clang::driver;
 using namespace clang::driver::tools;
 using namespace clang::driver::toolchains;
RocmInstallationDetector::getInstallationPathCandidates() {
   };
 
   // For candidate specified by --rocm-path we do not do strict check, i.e.,
   // checking existence of HIP version file and device library files.
   if (!RocmPathArg.empty()) {
     ROCmSearchDirs.emplace_back(RocmPathArg.str());
     DoPrintROCmSearchDirs();
     return ROCmSearchDirs;
-  } else if (const char *RocmPathEnv = ::getenv("ROCM_PATH")) {
-    if (!StringRef(RocmPathEnv).empty()) {
-      ROCmSearchDirs.emplace_back(RocmPathEnv);
+  } else if (Optional<std::string> RocmPathEnv =
+                 llvm::sys::Process::GetEnv("ROCM_PATH")) {
+    if (!RocmPathEnv->empty()) {
+      ROCmSearchDirs.emplace_back(std::move(*RocmPathEnv));
       DoPrintROCmSearchDirs();
       return ROCmSearchDirs;
     }
   }
 
   // Try to find relative to the compiler binary.
   const char *InstallDir = D.getInstalledDir();
 
if (DetectDeviceLib)
     detectDeviceLibrary();
 }
 
 void RocmInstallationDetector::detectDeviceLibrary() {
   assert(LibDevicePath.empty());
 
   if (!RocmDeviceLibPathArg.empty())
     LibDevicePath = RocmDeviceLibPathArg[RocmDeviceLibPathArg.size() - 1];
-  else if (const char *LibPathEnv = ::getenv("HIP_DEVICE_LIB_PATH"))
-    LibDevicePath = LibPathEnv;
+  else if (Optional<std::string> LibPathEnv =
+               llvm::sys::Process::GetEnv("HIP_DEVICE_LIB_PATH"))
+    LibDevicePath = std::move(*LibPathEnv);
 
   auto &FS = D.getVFS();
   if (!LibDevicePath.empty()) {
     // Maintain compatability with HIP flag/envvar pointing directly at the
     // bitcode library directory. This points directly at the library path instead
     // of the rocm root installation.
     if (!FS.exists(LibDevicePath))
       return;