👨‍💻📦 Build spdlog as a shared library on project installs (#1411)

## Description

Picked from #1403.
Builds `spdlog` as a shared library on library installs.
This reduces the wheel size from 14.3 MiB to 11.0 MiB on x86 linux.

## Checklist:

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- [x] The pull request only contains commits that are focused and
relevant to this change.
- [x] I have added appropriate tests that cover the new/changed
functionality.
- [x] I have updated the documentation to reflect these changes.
- [x] I have added entries to the changelog for any noteworthy
additions, changes, fixes, or removals.
- [x] I have added migration instructions to the upgrade guide (if
needed).
- [x] The changes follow the project's style guidelines and introduce no
new warnings.
- [x] The changes are fully tested and pass the CI checks.
- [x] I have reviewed my own code changes.

Signed-off-by: burgholzer <burgholzer@me.com>
Signed-off-by: Lukas Burgholzer <burgholzer@me.com>
(cherry picked from commit b9f6cf8)

Author: burgholzer

CHANGELOG.md

@@ -24,6 +24,7 @@ This project adheres to [Semantic Versioning], with the exception that minor rel
 
 ### Changed
 
+- 👨‍💻📦 Build `spdlog` as a shared library on project installs ([#1411]) ([**@burgholzer**])
 - ♻️🏁 Remove Windows-specific restrictions for dynamic QDMI device library handling ([#1406]) ([**@burgholzer**])
 - ♻️ Migrate Python bindings from `pybind11` to `nanobind` ([#1383]) ([**@denialhaag**], [**@burgholzer**])
 - 📦️ Provide Stable ABI wheels for Python 3.12+ ([#1383]) ([**@burgholzer**], [**@denialhaag**])
@@ -286,6 +287,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 
 <!-- PR links -->
 
+[#1411]: https://github.com/munich-quantum-toolkit/core/pull/1411
 [#1406]: https://github.com/munich-quantum-toolkit/core/pull/1406
 [#1402]: https://github.com/munich-quantum-toolkit/core/pull/1402
 [#1385]: https://github.com/munich-quantum-toolkit/core/pull/1385

cmake/ExternalDependencies.cmake

@@ -10,6 +10,7 @@
 
 include(FetchContent)
 include(CMakeDependentOption)
+include(GNUInstallDirs)
 set(FETCH_PACKAGES "")
 
 if(BUILD_MQT_CORE_BINDINGS)
@@ -94,15 +95,25 @@ set(SPDLOG_SYSTEM_INCLUDES
     ON
     CACHE INTERNAL "Treat the library headers like system headers")
 cmake_dependent_option(SPDLOG_INSTALL "Install spdlog library" ON "MQT_CORE_INSTALL" OFF)
+cmake_dependent_option(SPDLOG_BUILD_SHARED "Build spdlog as shared library" ON
+                       "BUILD_MQT_CORE_SHARED_LIBS" OFF)
 FetchContent_Declare(spdlog URL ${SPDLOG_URL} FIND_PACKAGE_ARGS ${SPDLOG_VERSION})
 list(APPEND FETCH_PACKAGES spdlog)
 
 # Make all declared dependencies available.
 FetchContent_MakeAvailable(${FETCH_PACKAGES})
 
+# Ensure external shared libraries end up in a common lib layout used by our RUNPATH
+if(TARGET spdlog)
+  set_target_properties(
+    spdlog
+    PROPERTIES LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR}"
+               ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR}"
+               RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_BINDIR}")
+endif()
+
 # Patch for spdlog cmake files to be installed in a common cmake directory
 if(SPDLOG_INSTALL)
-  include(GNUInstallDirs)
   install(
     CODE "
     file(GLOB SPDLOG_CMAKE_FILES

src/qdmi/na/CMakeLists.txt

@@ -26,7 +26,7 @@ if(NOT TARGET ${TARGET_NAME})
   target_sources(${TARGET_NAME} PUBLIC FILE_SET HEADERS BASE_DIRS ${MQT_CORE_INCLUDE_BUILD_DIR}
                                        FILES ${MQT_CORE_INCLUDE_BUILD_DIR}/qdmi/na/Generator.hpp)
 
-  # Link nlohmann_json, spdlog
+  # Link nlohmann_json and spdlog
   target_link_libraries(
     ${TARGET_NAME}
     PUBLIC nlohmann_json::nlohmann_json

src/qdmi/sc/CMakeLists.txt

@@ -26,7 +26,7 @@ if(NOT TARGET ${TARGET_NAME})
   target_sources(${TARGET_NAME} PUBLIC FILE_SET HEADERS BASE_DIRS ${MQT_CORE_INCLUDE_BUILD_DIR}
                                        FILES ${MQT_CORE_INCLUDE_BUILD_DIR}/qdmi/sc/Generator.hpp)
 
-  # Link nlohmann_json, spdlog
+  # Link nlohmann_json and spdlog
   target_link_libraries(
     ${TARGET_NAME}
     PUBLIC nlohmann_json::nlohmann_json