Fix GHSA-94p6-54jq-9mwp

Apache only generates REDIRECT_STATUS, so explicitly check for that
if the server name is Apache, don't allow other variable names.
Furthermore, redirect.so and Netscape no longer exist, so
remove those entries as we can't check their server name anymore.

We now also check for the configuration override *first* such that it
always take precedence. This would allow for a mitigation path if
something like this happens in the future.

Author: ndossche

sapi/cgi/cgi_main.c

@@ -1885,18 +1885,17 @@ int main(int argc, char *argv[])
 
 	/* check force_cgi after startup, so we have proper output */
 	if (cgi && CGIG(force_redirect)) {
-		/* Apache will generate REDIRECT_STATUS,
-		 * Netscape and redirect.so will generate HTTP_REDIRECT_STATUS.
-		 * redirect.so and installation instructions available from
-		 * http://www.koehntopp.de/php.
-		 *   -- kk@netuse.de
-		 */
-		if (!getenv("REDIRECT_STATUS") &&
-			!getenv ("HTTP_REDIRECT_STATUS") &&
-			/* this is to allow a different env var to be configured
-			 * in case some server does something different than above */
-			(!CGIG(redirect_status_env) || !getenv(CGIG(redirect_status_env)))
-		) {
+		/* This is to allow a different environment variable to be configured
+		 * in case the we cannot auto-detect which environment variable to use.
+		 * Checking this first to allow user overrides in case the environment
+		 * variable can be set by an untrusted party. */
+		const char *redirect_status_env = CGIG(redirect_status_env);
+		if (!redirect_status_env) {
+			/* Apache will generate REDIRECT_STATUS. */
+			redirect_status_env = "REDIRECT_STATUS";
+		}
+
+		if (!getenv(redirect_status_env)) {
 			zend_try {
 				SG(sapi_headers).http_response_code = 400;
 				PUTS("<b>Security Alert!</b> The PHP CGI cannot be accessed directly.\n\n\