perf tools: Preserve identifier id in OCaml demangler

Some OCaml developers reported that this bit of information is sometimes
useful for disambiguating functions for which the OCaml compiler assigns
the same name, e.g. nested or inlined functions.

Signed-off-by: Fabian Hemmer <copy@copy.sh>
Link: http://lore.kernel.org/lkml/20210226075223.p3s5oz4jbxwnqjtv@nyu


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>