[MC] Make .pseudo_probe created 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, two
elements may sit in two different allocations from BumpPtrAllocator, with
an unpredictable order. Under tcmalloc,
llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll fails about 7 times per
1000 runs.