[svn r305] Started support for custom class allocators/deallocators. Allocators with more than one argument still need to be fixed.

Removed the LLVM stacktrace code from mars.c.
Moved the LLVM based default target detection code from mars.c to llvmhelpers.cpp.

gen/toir.cpp

@@ -1885,10 +1885,7 @@ DValue* NewExp::toElem(IRState* p)
     Logger::print("NewExp::toElem: %s | %s\n", toChars(), type->toChars());
     LOG_SCOPE;
 
-    assert(!newargs && "arguments to new not yet supported");
     assert(newtype);
-    assert(!allocator && "custom allocators not yet supported");
-
     Type* ntype = DtoDType(newtype);
 
     // new class