[benaliabderrahmane]

Problem

On Rolling, colcon build aborts at CMake configure time, before any source compiles:

-- Performing Test RMW_HAS_LOCALHOST_ONLY
No known features for C compiler
  "" version .
Failed to generate test project build system.

The RMW_HAS_LOCALHOST_ONLY probe (commit fb9ee3d) runs check_cxx_source_compiles(...) with CMAKE_REQUIRED_LIBRARIES = rmw::rmw rcutils::rcutils, which links those imported targets into a CXX-only scratch project. rcutils is a C library whose exported target now carries a C INTERFACE_COMPILE_FEATURES; resolving a C compile feature in a project where the C language was never enabled makes the inner try_compile fail to generate. This is upstream drift — the same CMakeLists.txt passed Rolling on 2026-06-01, and jazzy/kilted are unaffected.

Fix

The probe only needs the rmw headers (it references the type + a macro and links nothing). Feed it the rmw and rcutils include dirs via CMAKE_REQUIRED_INCLUDES instead of linking the targets — no imported target is linked, so no C compile-feature is pulled into the CXX scratch project. (rmw/init_options.h transitively includes rcutils/allocator.h, hence both include dirs.)

Verified

• Local clean build on jazzy (rmw 7.3.3, field present): probe correctly detects it → -DRMW_HAS_LOCALHOST_ONLY=1, builds clean with 0 warnings.
• Field presence by distro: jazzy 7.3.3 has localhost_only; kilted 7.8.2 and rolling 7.10.1 do not (removed at rmw 7.8) — the probe resolves correctly on each.

Independent of the audit-fix PRs (#4–#9); fixes Rolling CI for all of them once merged.