fix a tricky bug in the JIT global variable emitter, that was triggered when JITing a variable independently of a function. This lead to sharing memory memory between functions and GVs thus changing the value of a GV could change the code in execution. more details on the ML.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57900 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineCodeEmitter.h

@@ -207,7 +207,7 @@ public:
   /// allocateSpace - Allocate a block of space in the current output buffer,
   /// returning null (and setting conditions to indicate buffer overflow) on
   /// failure.  Alignment is the alignment in bytes of the buffer desired.
-  void *allocateSpace(intptr_t Size, unsigned Alignment) {
+  virtual void *allocateSpace(intptr_t Size, unsigned Alignment) {
     emitAlignment(Alignment);
     void *Result = CurBufferPtr;