On IBM Z the Boost tagged pointer implementation cannot use
"pointer compression" as there are no unused bits in an address;
the whole 64-bit address space is available to user space code.
Instead, Boost uses 16-byte atomics. This is always supported
on IBM Z, but depending on the particular compiler (version)
it may require linking against libatomic. The existing checks
in CheckCxxAtomic.cmake do not catch this, however, as they only
test for (up to) 8-byte atomic support.
Fixed by adding a test for 16-byte atomic support on IBM Z.
Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>
for instance, GCC-8 on riscv64 does not offer atomic ops like
__atomic_fetch_or_1, so we need to link against libatomic to get access
to these symbols.
Signed-off-by: Kefu Chai <kchai@redhat.com>
