Shell: Explicitly declare 'environ' to make the macOS Lagom build happy

Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/cd8495f1d4b
Pull-request: https://github.com/SerenityOS/serenity/pull/2799

Shell/Builtin.cpp

@@ -31,7 +31,9 @@
 #include <inttypes.h>
 #include <signal.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
+extern char** environ;
 extern RefPtr<Line::Editor> editor;
 
 int Shell::builtin_alias(int argc, const char** argv)

Shell/Shell.cpp

@@ -52,6 +52,7 @@
 
 static bool s_disable_hyperlinks = false;
 extern RefPtr<Line::Editor> editor;
+extern char** environ;
 
 //#define SH_DEBUG