cmd/compile: fix duplicated dwarf parameters for some functions

[mauri870]

Dwarf formal parameters appear more than once in the
final dwarf symbols for some functions. I believe there is an error
up the chain where the vars are created and some of them are pushed
more than once to the list.

I ended up implementing a simple dedup mechanism to get rid of the
duplicates up the chain, but this should be investigated deeper in
a follow up ticket in order to find the root cause.

The testing routine findSubprogramDIE was updated to panic in case it
received duplicated formal parameters since this bug probably existed
for quite a while and it was never discovered since this function
basically pushes into a map indexed by the var name, overwriting the
last value.

A test has been added to cover this case as reported in the original
issue ticket.

Fixes #61357

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Message from Mauri de Souza Meneguzzo:

Patch Set 3:

(1 comment)

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Message from [email protected]:

Patch Set 4:

(1 comment)

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Message from Mauri de Souza Meneguzzo:

Patch Set 4:

(1 comment)

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Message from Mauri de Souza Meneguzzo:

Patch Set 6: Run-TryBot+1

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Patch Set 6:

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Message from Mauri de Souza Meneguzzo:

Patch Set 6:

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Patch Set 6:

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Message from Gopher Robot:

Patch Set 6: TryBot-Result-1

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