Allow multiple declarations to share the same mangled name/LLVM global.

This is necessary to enable aliasing compiler-generated
symbols with pragma(mangle, …).

Note that globals for internal use are still directly
created.

gen/classes.cpp

@@ -605,7 +605,8 @@ static LLConstant* build_offti_array(ClassDeclaration* cd, LLType* arrayT)
     name.append("__OffsetTypeInfos");
 
     // create symbol
-    llvm::GlobalVariable* gvar = new llvm::GlobalVariable(arrTy,true,DtoInternalLinkage(cd),arrInit,name,gIR->module);
+    llvm::GlobalVariable* gvar = getOrCreateGlobal(cd->loc, *gIR->module, arrTy,
+        true,DtoInternalLinkage(cd),arrInit,name);
     ptr = DtoBitCast(gvar, getPtrToType(arrTy->getElementType()));
 
     return DtoConstSlice(size, ptr);