As submitted upstream in a review, avoid using undefined behavior in
llvm's LinkAllPasses.h. This caused some of the calls not to be
emitted, if the optimization level was -O2 or higher.

Conversely, if you used -O1 or lower, calls to e.g. RunningOnValgrind()
would be emitted, leading to link failures, because we did not include
Valgrind.cpp into libllvmsupport. Therefore, add it unconditionally.

Noticed by: ian