Merge pull request #4603 from modelica/maltelenz-unforced-installprefix

Only force CMAKE_INSTALL_PREFIX if the user didn't specify it.

Author: maltelenz

Modelica/Resources/CMakeLists.txt

@@ -17,11 +17,14 @@ set(MODELICA_UTILITIES_INCLUDE_DIR "${MODELICA_RESOURCES_DIR}/C-Sources")
 include(BuildProjects/CMake/Modelica_platform.cmake)
 include(BuildProjects/CMake/Modelica_utilities.cmake)
 
-set(
-  CMAKE_INSTALL_PREFIX "${MODELICA_RESOURCES_DIR}"
-  CACHE PATH
-  "Library installation prefix path (don't change)" FORCE
-)
+# Do not override CMAKE_INSTALL_PREFIX if it was set by the user. CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT is automatically provided by cmake.
+if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+  set(
+    CMAKE_INSTALL_PREFIX "${MODELICA_RESOURCES_DIR}"
+    CACHE PATH
+    "Library installation prefix path (don't change)" FORCE
+  )
+endif()
 
 get_modelica_platform_name_with_compiler_version(MODELICA_PLATFORM_NAME)
 set(