rename ENABLE_THREADS to LLVM_ENABLE_THREADS

Now that it needs to be exported in a public header (Valgrind.h)
it should be prefixed to avoid collision with other projects.
Add it to llvm-config.h as well.

This'll require regenerating the configure script after this
commit, but I don't have the required autoconf version.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145214 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Threading.cpp b/lib/Support/Threading.cpp
index 8f0bb93..7483225 100644
--- a/lib/Support/Threading.cpp
+++ b/lib/Support/Threading.cpp
@@ -24,7 +24,7 @@
 static sys::Mutex* global_lock = 0;
 
 bool llvm::llvm_start_multithreaded() {
-#if ENABLE_THREADS != 0
+#if LLVM_ENABLE_THREADS != 0
   assert(!multithreaded_mode && "Already multithreaded!");
   multithreaded_mode = true;
   global_lock = new sys::Mutex(true);
@@ -39,7 +39,7 @@
 }
 
 void llvm::llvm_stop_multithreaded() {
-#if ENABLE_THREADS != 0
+#if LLVM_ENABLE_THREADS != 0
   assert(multithreaded_mode && "Not currently multithreaded!");
 
   // We fence here to insure that all threaded operations are complete BEFORE we
@@ -63,7 +63,7 @@
   if (multithreaded_mode) global_lock->release();
 }
 
-#if ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
+#if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
 #include <pthread.h>
 
 struct ThreadInfo {
@@ -102,7 +102,7 @@
  error:
   ::pthread_attr_destroy(&Attr);
 }
-#elif ENABLE_THREADS!=0 && defined(LLVM_ON_WIN32)
+#elif LLVM_ENABLE_THREADS!=0 && defined(LLVM_ON_WIN32)
 #include "Windows/Windows.h"
 #include <process.h>