Fix shared compilation on macOS

[iamluc]

Description

Fix compilation of the rust crate on macOS when using the php_shared_build config option.

Error was:

  = note: Undefined symbols for architecture arm64:
            "_DDTRACE_MOCK_PHP", referenced from:
                _ddog_sidecar_connect_php in ddtrace_php.ddtrace_php.5b56db22beb5c715-cgu.0.rcgu.o
            "_DDTRACE_MOCK_PHP_SIZE", referenced from:
                _ddog_sidecar_connect_php in ddtrace_php.ddtrace_php.5b56db22beb5c715-cgu.0.rcgu.o
          ld: symbol(s) not found for architecture arm64
          clang: error: linker command failed with exit code 1 (use -v to see invocation)

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

Merging #2613 (f93b642) into master (633c5ad) will decrease coverage by 1.96%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2613      +/-   ##
============================================
- Coverage     76.53%   74.57%   -1.96%     
  Complexity     2609     2609              
============================================
  Files           217      217              
  Lines         23318    23318              
============================================
- Hits          17846    17389     -457     
- Misses         5472     5929     +457     

Flag	Coverage Δ
tracer-extension	78.70% <ø> (ø)
tracer-php	69.50% <ø> (-4.37%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 14 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 633c5ad...f93b642. Read the comment docs.