Update dd-trace-cpp

[xlamorlette-datadog]

It was needed to update dd-trace-cpp because the local build was failing because of a too old version of nlohmann/json.

Details About the Old nlohmann/json Dependency Issue

We got:

cmake -B build -DCMAKE_BUILD_TYPE=Release -DHTTPD_SRC_DIR=httpd .
[…]
CMake Error at build/_deps/json-src/CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.

This came from deps/dd-trace-cpp/cmake/deps/json.cmake:

  URL https://github.com/nlohmann/json/releases/download/v3.11.2/json.tar.xz

which was actually incoherent with deps/dd-trace-cpp/src/datadog/json.hpp:

// |  |  |__   |  |  | | | |  version 3.12.0

Tricky Technical Change for Linking dd-trace-cpp

In October 2025, dd-trace-cpp introduced the following building change, line 229 of CMakeLists.txt:

set_target_properties(dd-trace-cpp-objects
  PROPERTIES
    VERIFY_INTERFACE_HEADER_SETS ON
    POSITION_INDEPENDENT_CODE ${BUILD_SHARED_LIBS}
)

This makes POSITION_INDEPENDENT_CODE on only when building a shared lib.
But in the Apache plugin, we use the static library that gets linked into mod_datadog.so, which is loaded via dlopen. And any object file that ends up in .so file loaded via dlopen must be compiled with -fPIC, even when going through a static library intermediary. (Else, we get a linker error because initial-exec TLS relocation are incompatible with dlopen.)
This is fixed by overriding POSITION_INDEPENDENT_CODE after add_subdirectory(dd-trace-cpp) in deps/CMakeLists.txt.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.12%. Comparing base (43b48ff) to head (bf29d88).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #45   +/-   ##
=======================================
  Coverage   63.12%   63.12%           
=======================================
  Files           7        7           
  Lines         377      377           
  Branches       49       49           
=======================================
  Hits          238      238           
  Misses        101      101           
  Partials       38       38           

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