Add a declaration of environ global for Darwin

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16100 91177308-0d34-0410-b5e6-96231b3b80d8

lib/System/Unix/Program.cpp

@@ -24,6 +24,8 @@
 #include <sys/wait.h>
 #endif
 
+extern char** environ;
+
 namespace llvm {
 using namespace sys;
 

lib/System/Unix/Program.inc

@@ -24,6 +24,8 @@
 #include <sys/wait.h>
 #endif
 
+extern char** environ;
+
 namespace llvm {
 using namespace sys;