Add OpenVR SDK to third_party

third_party/openvr/src/src/vrcommon/envvartools_public.cpp

Index: third_party/openvr/src/src/vrcommon/envvartools_public.cpp
diff --git a/third_party/openvr/src/src/vrcommon/envvartools_public.cpp b/third_party/openvr/src/src/vrcommon/envvartools_public.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..987bceb0257e41501f86b607cf792199fbe9081a
--- /dev/null
+++ b/third_party/openvr/src/src/vrcommon/envvartools_public.cpp
@@ -0,0 +1,46 @@
+//========= Copyright Valve Corporation ============//
+#include "envvartools_public.h"
+#include <stdlib.h>
+
+#if defined(_WIN32)
+#include <Windows.h>
+
+#undef GetEnvironmentVariable
+#undef SetEnvironmentVariable
+#endif
+
+
+std::string GetEnvironmentVariable( const char *pchVarName )
+{
+#if defined(_WIN32)
+	char rchValue[32767]; // max size for an env var on Windows
+	DWORD cChars = GetEnvironmentVariableA( pchVarName, rchValue, sizeof( rchValue ) );
+	if( cChars == 0 )
+		return "";
+	else
+		return rchValue;
+#elif defined(POSIX)
+	char *pchValue = getenv( pchVarName );
+	if( pchValue )
+		return pchValue;
+	else
+		return "";
+#else
+#error "Unsupported Platform"
+#endif
+}
+
+
+bool SetEnvironmentVariable( const char *pchVarName, const char *pchVarValue )
+{
+#if defined(_WIN32)
+	return 0 != SetEnvironmentVariableA( pchVarName, pchVarValue );
+#elif defined(POSIX)
+	if( pchVarValue == NULL )
+		return 0 == unsetenv( pchVarName );
+	else
+		return 0 == setenv( pchVarName, pchVarValue, 1 );
+#else
+#error "Unsupported Platform"
+#endif
+}