runtime: re-order environment variable lookup

Hoist the no environment case over the case with the environment. This
ensures that if no environment configuration is selected, the code still
builds. If no environment configuration is selected, `ENVIRON` may still
be defined and that results in calls to elided functions.

Author: compnerd

stdlib/public/runtime/EnvironmentVariables.cpp

@@ -187,7 +187,11 @@ extern "C" char **_environ;
 #endif
 #endif
 
-#ifdef ENVIRON
+#if !SWIFT_STDLIB_HAS_ENVIRON
+void swift::runtime::environment::initialize(void *context) {
+  (void)context;
+}
+#elif defined(ENVIRON)
 void swift::runtime::environment::initialize(void *context) {
   // On platforms where we have an environment variable array available, scan it
   // directly. This optimizes for the common case where no variables are set,
@@ -241,7 +245,7 @@ void swift::runtime::environment::initialize(void *context) {
   if (SWIFT_DEBUG_HELP_variable)
     printHelp(nullptr);
 }
-#elif SWIFT_STDLIB_HAS_ENVIRON
+#else
 void swift::runtime::environment::initialize(void *context) {
   // Emit a getenv call for each variable. This is less efficient but works
   // everywhere.
@@ -259,10 +263,6 @@ void swift::runtime::environment::initialize(void *context) {
     printHelp("Using getenv to read variables. Unknown SWIFT_DEBUG_ variables "
               "will not be flagged.");
 }
-#else
-void swift::runtime::environment::initialize(void *context) {
-  (void)context;
-}
 #endif
 
 SWIFT_RUNTIME_EXPORT