R600: Set the noduplicate attribute on barrier() intrinsics

This will prevent LLVM optimization passes from creating illegal uses
of the barrier() intrinsic (e.g. calling barrier() from a conditional
that is not executed by all threads).
s/_CLC_DECL/_CLC_DEF/

Some function definitions were using _CLC_DECL, which meant that they
weren't being marked as always_inline.

Reviewed-by and Tested-by: Aaron Watry <awatry@gmail.com>
[msan] Disable mlock/mlockall to work around a linux kernel bug.

The same logic is present in ASan and TSan.