Add getenv() wrapper that works on multibyte environment variable.

On Windows, character encoding of multibyte environment variable varies
depending on settings. The only reliable way to handle it I think is to use
GetEnvironmentVariableW().

GetEnvironmentVariableW() works on wchar_t string, which is on Windows UTF16
string. That's not ideal because we use UTF-8 as the internal encoding in LLVM.
This patch defines a wrapper function which takes and returns UTF-8 string for
GetEnvironmentVariableW().

The wrapper function does not do any conversion and just forwards the argument
to getenv() on Unix.

Differential Revision: http://llvm-reviews.chandlerc.com/D1612

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190423 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Support/ProcessTest.cpp b/unittests/Support/ProcessTest.cpp
index eff9c71..ac1b01e 100644
--- a/unittests/Support/ProcessTest.cpp
+++ b/unittests/Support/ProcessTest.cpp
@@ -39,4 +39,32 @@
   EXPECT_GT(TimeValue::MaxTime, process::get_self()->get_wall_time());
 }
 
+#ifdef LLVM_ON_WIN32
+#define setenv(name, var, ignore) _putenv_s(name, var)
+#endif
+
+#if HAVE_SETENV || defined(LLVM_ON_WIN32)
+TEST(ProcessTest, Basic) {
+  setenv("__LLVM_TEST_ENVIRON_VAR__", "abc", true);
+  Optional<std::string> val(Process::GetEnv("__LLVM_TEST_ENVIRON_VAR__"));
+  EXPECT_TRUE(val.hasValue());
+  EXPECT_STREQ("abc", val->c_str());
+}
+
+TEST(ProcessTest, None) {
+  Optional<std::string> val(
+      Process::GetEnv("__LLVM_TEST_ENVIRON_NO_SUCH_VAR__"));
+  EXPECT_FALSE(val.hasValue());
+}
+#endif
+
+#ifdef LLVM_ON_WIN32
+TEST(ProcessTest, Wchar) {
+  SetEnvironmentVariableW(L"__LLVM_TEST_ENVIRON_VAR__", L"abcdefghijklmnopqrs");
+  Optional<std::string> val(Process::GetEnv("__LLVM_TEST_ENVIRON_VAR__"));
+  EXPECT_TRUE(val.hasValue());
+  EXPECT_STREQ("abcdefghijklmnopqrs", val->c_str());
+}
+#endif
+
 } // end anonymous namespace