[NO-TICKET] Fix profiler inline helpers not working when optimization disabled

[ivoanjo]

What does this PR do?

This PR makes sure that every inline helper in the profile is marked as static inline.

As documented in https://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline:

When a function is both inline and static, if all calls to the function
are integrated into the caller, and the function’s address is never
used, then the function’s own assembler code is never referenced.

this is different from just inline:

When an inline function is not static, then the compiler must assume
that there may be calls from other source files; since a global
symbol can be defined only once in any program, the function must not
be defined in the other source files, so the calls therein cannot
be integrated. Therefore, a non-static inline function is always
compiled on its own in the usual fashion.

In practice, this manifested as errors such as

symbol lookup error: datadog_profiling_native_extension.3.4.0_x86_64-linux.so:
undefined symbol: monotonic_wall_time_now_ns

when building Ruby or the profiler with optimization disabled (-O0).

With this fix, these errors no longer show up when building with optimization disabled.

Motivation:

Avoid runtime failures in the profiler on Ruby builds with optimization disabled / when debugging the profiler.

Additional Notes:

Most of these methods with only inline were still unreleased to customers so hopefully nobody was impacted by this issue.

For consistency, I've also made sure that all methods are static inline as we had a mix of inline static as well.

How to test the change?

I was able to trigger the issue by running

$ DDTRACE_DEBUG=true bundle exec rake clean compile
$ bundle exec rspec spec/datadog/profiling/

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.85%. Comparing base (84e92fa) to head (0ca54ec).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3856      +/-   ##
==========================================
- Coverage   97.86%   97.85%   -0.02%     
==========================================
  Files        1271     1271              
  Lines       75975    75975              
  Branches     3739     3739              
==========================================
- Hits        74352    74343       -9     
- Misses       1623     1632       +9     

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[pr-commenter]

Benchmarks

Benchmark execution time: 2024-08-21 14:07:23

Comparing candidate commit 0ca54ec in PR branch ivoanjo/fix-use-of-inline with baseline commit 84e92fa in branch master.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 21 metrics, 2 unstable metrics.

scenario:profiler - sample timeline=false

• 🟥 throughput [-0.752op/s; -0.717op/s] or [-10.347%; -9.868%]

scenario:profiler - stack collector

• 🟥 throughput [-153.919op/s; -152.423op/s] or [-4.983%; -4.935%]