[MC] Make .pseudo_probe sections deterministic after D91878

MCPseudoProbeSections::emit iterates over MCProbeDivisions and creates sections.
When the map key is MCSymbol *, the iteration order is not stable. The
underlying BumpPtrAllocator largely decreases the flakiness. That said,
the allocations from BumpPtrAllocator may have different orders.
Under tcmalloc, llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll fails
about 7 times per 1000 runs.