Let us start here, from square one. No, from Zero!

external/openvr/src/vrcommon/envvartools_public.h

@@ -0,0 +1,8 @@
+//========= Copyright Valve Corporation ============//
+#pragma once
+
+#include <string>
+
+std::string GetEnvironmentVariable( const char *pchVarName );
+bool GetEnvironmentVariableAsBool( const char *pchVarName, bool bDefault );
+bool SetEnvironmentVariable( const char *pchVarName, const char *pchVarValue );