fix: prefix vendored mpack symbols

[jpnurmi]

Similar to getsentry/crashpad#143, but in C, we don't have namespaces, so the symbol rename comes with some less-nice define trickery... Includes a test to catch unprefixed mpack symbols:

$ tests/test_build_static.py::test_static_mpack
...
FAILED tests/test_build_static.py::test_static_mpack - AssertionError: libsentry.a contains 322 unprefixed MPack symbols: mpack_discard, mpack_done_array, mpack_done_bin, mpack_done_map, mpack_done_str, mpack_done_type, mpack_error_to_string, mpack_expect_array, mpack_expect_array_alloc_impl, mpack_expect_array_match

Close: #1878

[jpnurmi]

this is quite ugly but i still find it better than the alternative of prefixing all symbols in the vendored mpack sources. we should upgrade to the latest mpack, and then it gets painful if ours is heavily modified...

Note

Sentry Native vendors MPack 1.0, released upstream on October 20, 2018—about 7 years and 9 months old today: ludocode/mpack@e150cb7

It was imported into Sentry Native on February 24, 2020, with the Crashpad integration—about 6 years and 5 months ago: e4bed02

It has never been upgraded from 1.0. The vendored files only received two local patches:

• September 15, 2020: work around missing _Static_assert support in MSVC: f143733
• July 23, 2024: use Sentry’s allocator for MPack allocations: e58b655

The latest upstream release remains MPack 1.1.1 from January 2023.

[codecov]

Codecov Report

❌ Patch coverage is 34.57447% with 123 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.15%. Comparing base (88e7bae) to head (396dd4c).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1880      +/-   ##
==========================================
- Coverage   75.56%   75.15%   -0.42%     
==========================================
  Files          90       91       +1     
  Lines       21154    21342     +188     
  Branches     3759     3759              
==========================================
+ Hits        15986    16040      +54     
- Misses       4334     4476     +142     
+ Partials      834      826       -8     

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[JoshuaMoelans]

nice, lgtm