Revert "[ARM, Fix] Fix emitLeading/TrailingFence on old ARM processors"

It is breaking the build on the buildbots but works fine on my machine, I revert
while trying to understand what happens (it appears to depend on the compiler used
to build, I probably used a C++11 feature that is not perfectly supported by some
of the buildbots).

This reverts commit feb3176c4d006f99af8b40373abd56215a90e7cc.

llvm-svn: 217973