[lsan] ppc64: dynamically pick address range for allocator

For ppc64 PIE, it seems that [0xa00000000000,0xc00000000000) may be occupied
which will lead to a segfault in certain kernel configurations
(clang-ppc64le-rhel). Use the `!kUsingConstantSpaceBeg` code path like Fuchsia.

Reviewed By: jsji

Differential Revision: https://reviews.llvm.org/D121257