build: ship libosrm as a CMake Config Package

[tete17]

Summary

Replace the hand-rolled example/cmake/FindLibOSRM.cmake find-module with a proper CMake Config Package, matching the pattern used by every modern C++ library we already depend on via vcpkg (flatbuffers, fmt, nlohmann_json, protozero, TBB).

Before

Downstream CMake consumers had to copy example/cmake/FindLibOSRM.cmake into their project and prepend it to CMAKE_MODULE_PATH. That find-module was a pkg-config wrapper that returned flag-string variables — no imported targets, no transitive usage requirements, no auto-discovery.

After

find_package(LibOSRM REQUIRED)
target_link_libraries(myapp PRIVATE osrm::osrm)

No CMAKE_MODULE_PATH tweak, no pkg-config, no manual find_package() calls for transitive deps — LibOSRMConfig.cmake re-declares Boost, TBB, Threads, and ZLIB via find_dependency() on behalf of the consumer.

How it works

• New cmake/LibOSRMConfig.cmake.in template consumed by configure_package_config_file(); paired with write_basic_package_version_file(VERSION ${OSRM_VERSION} COMPATIBILITY SameMinorVersion) so consumers can use version ranges.
• install(TARGETS osrm ... EXPORT LibOSRMTargets ...) + install(EXPORT LibOSRMTargets NAMESPACE osrm::) writes lib/cmake/LibOSRM/LibOSRMTargets.cmake with the imported target's IMPORTED_LOCATION, INTERFACE_INCLUDE_DIRECTORIES, and INTERFACE_LINK_LIBRARIES baked in.
• target_include_directories(osrm INTERFACE ...) exposes the public include dir via BUILD_INTERFACE (subproject builds) and two INSTALL_INTERFACE entries — both include and include/osrm — so consumer code using either #include <osrm/...> or the internal "engine/api/..." non-prefixed paths resolves correctly after install.
• ZLIB_LIBRARY and CMAKE_THREAD_LIBS_INIT replaced with their imported-target equivalents (ZLIB::ZLIB, Threads::Threads) so ENGINE_LIBRARIES serialises cleanly into LibOSRMTargets.cmake instead of absolute file paths that would be non-portable across install prefixes.
• example/CMakeLists.txt rewritten from variable-splicing dance down to find_package(LibOSRM) + target_link_libraries(... osrm::osrm).
• example/cmake/FindLibOSRM.cmake deleted.

Scope

Only osrm (the routing engine) is exposed as a Config Package target — same scope as the deleted find-module. The other six osrm_* libraries remain build-internal support for the CLI tools and keep their existing plain install(TARGETS ... DESTINATION lib) rules. Exposing them as imported targets would require modernising OSMIUM_LIBRARIES / EXPAT / BZIP2 / LUA to imported targets, which is left for a follow-up.

libosrm.pc is kept as-is for Make/Meson/autotools consumers that have no CMake.

Net diff: +74 / -72 across 4 files.

Test plan

• cmake --install to a scratch prefix produces the four expected files under lib/cmake/LibOSRM/ (Config, ConfigVersion, Targets, Targets-release).
• A fresh consumer project (stripped copy of example/) with only CMAKE_PREFIX_PATH pointed at the scratch prefix configures, compiles, and links osrm-example against osrm::osrm without any other hints.
• CI green on all platforms.

[Copilot]

Pull request overview

This PR modernizes downstream consumption of libosrm by replacing the old FindLibOSRM.cmake find-module (pkg-config wrapper + flag variables) with a proper installed CMake Config Package that exposes an imported target (osrm::osrm) and re-finds transitive dependencies for consumers.

Changes:

• Install/export osrm via LibOSRMTargets.cmake and generate/install LibOSRMConfig.cmake + LibOSRMConfigVersion.cmake.
• Update the example/ consumer to use find_package(LibOSRM) + target_link_libraries(... osrm::osrm).
• Delete the legacy example/cmake/FindLibOSRM.cmake module.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
CMakeLists.txt	Adds exported install set + config/version package generation; adjusts include dirs and switches some deps to imported targets.
cmake/LibOSRMConfig.cmake.in	New installed package config template that re-finds dependencies and includes exported targets.
example/CMakeLists.txt	Simplifies example consumer to link against osrm::osrm via find_package(LibOSRM).
example/cmake/FindLibOSRM.cmake	Removes legacy find-module.

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[DennisOSRM]

Does this change the API, ie. does it require changes in the code bases that embed OSRM?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.82%. Comparing base (b9d7303) to head (1214178).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7524      +/-   ##
==========================================
- Coverage   90.83%   90.82%   -0.01%     
==========================================
  Files         484      484              
  Lines       37816    37816              
==========================================
- Hits        34350    34348       -2     
- Misses       3466     3468       +2     

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