lib/58840: expat leaks internal symbols

[campbell+netbsd%mumble.net@localhost]

>Number:         58840
>Category:       lib
>Synopsis:       expat leaks internal symbols
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Nov 21 21:20:01 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current, 10, 9, ...
>Organization:
The NexpatBSymbolD Excess
>Environment:
>Description:
Upstream builds libexpat.so with -fvisibility=hidden and marks exported symbols explicitly, but we don't pass -fvisibility=hidden so various internal symbols leak out:

_INTERNAL_trim_to_complete_utf8_characters
testingAccountingGetCountBytesDirect
testingAccountingGetCountBytesIndirect
unsignedCharToPrintable

>How-To-Repeat:
nm, code inspection
>Fix:
Like with libarchive (PR lib/58829: libarchive exports excess symbols, https://gnats.NetBSD.org/58829), we should build with -fvisibility=hidden although this means dropping some symbols in the current library.