Double minus in front of overflown enumerator

[pmachata]

Source:

enum N{A=9223372036854775808UL};
template<N n>class gah{};
gah<A> meh;

Object (compiler can be gleaned from DW_AT_producer):

$ gzip -c gah3.o | base64 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Output:

$ ./dwgrep/dwgrep ~/tmp/gah3.o -e 'entry ?TAG_template_value_parameter'
[41]    template_value_parameter
    name (string)   n;
    type (ref4) [1d];
    const_value (sdata) --9223372036854775808;

[pmachata]

A simpler test case:

$ ./dwgrep/dwgrep -e '-0x8000000000000000 dec'
--9223372036854775808