Improve handling of linked libraries to generated CPP code. (#11143)

  - This will only affect omc compiled with the CMake build system.

  - Handle things like boost libraries a bit better. This is intended to
    fix only Linux and Windows with OMDev builds. Compiling generated CPP
    code with MSVC has many issues and there was no attempt to consider it
    in these changes. It can come later.

  - Try documenting some of the variables.

Author: mahge

OMCompiler/SimulationRuntime/cpp/Core/CMakeLists.txt

@@ -1,29 +1,52 @@
 
-macro(target_public_headers TARGET)
-    set_target_properties(${TARGET} PROPERTIES PUBLIC_HEADER "${ARGN}")
-endmacro()
 
+#####################################################################################################
+# Configure and generate the files 'ModelicaLibraryConfig_gcc.inc' and 'ModelicaConfig_gcc.inc'
+# These files tell the CPP code generator what name to use and where to find the necessary
+# libraries for the generated simulation code. This does not cover all variables that are used
+# or set by the old CPP-runtime build system. However, these seem to be enough to build things
+# on Linux and Windows with OMDev.
+
+# SCOREP_INCLUDE_ is added to the compilation command-line of the generated code (in the Makefiles).
+# It is not clear why this one is chosen among the many others to be explicitly added to the generated
+# compilation code. It needs to be set to a valid directory resembling path.
 set(SCOREP_INCLUDE_ ".")
+
+# The boost libraries and headers are expected to be in the system directories.
+# For MSVC this needs to be adjusted. However, it is not clear which approach we are
+# taking for MSVC yet. So leave it like this until we decide.
 set(Boost_INCLUDE_ ".")
+# This is supposwed to signify the directory where the boost libraries can be found (for -L ...)
 set(Boost_LIBS_ ".")
+# The actual boost libraries needed to be linked.
+set(Boost_LIBRARIES_ "-lboost_program_options -lboost_filesystem")
+
+# Lapack libs are also expected to be in the system directories.
 set(LAPACK_LIBS_ ".")
-set(SYSTEM_CFLAGS ${SYSTEM_CFLAGS} "-DOMC_BUILD -fPIC -DUSE_THREAD")
 if(UNIX)
   set(LAPACK_LIBRARIES_ "-llapack -lblas")
-else()
-  set(LAPACK_LIBRARIES_ "")
+  set(LINUX_LIB_DL "-ldl")
 endif()
 
+# The thread library flag (can be something like -lpthreads for example). Let CMake decide the value.
+set(CPPTHREADS_LIBRARY_FLAG ${CMAKE_THREAD_LIBS_INIT})
+
+# Some common flags for the generated simulation code. It is not clear why OMC_BUILD is defined
+# by the old system. It is always defined for some reason. USE_THREAD means use the C++ standard
+# library's thread library (instead of something like boost threads).
+set(SYSTEM_CFLAGS ${SYSTEM_CFLAGS} "-DOMC_BUILD -DUSE_THREAD -fPIC")
+
+# Configure the files.
 configure_file(Modelica/ModelicaLibraryConfig_gcc.inc.in ${CMAKE_CURRENT_BINARY_DIR}/ModelicaLibraryConfig_gcc.inc)
 configure_file(Modelica/ModelicaConfig_gcc.inc.in ${CMAKE_CURRENT_BINARY_DIR}/ModelicaConfig_gcc.inc)
 
+# Install them during installtion. They end up in the appropriate include directory. Right now that is 'include/cpp'.
 install (FILES ${CMAKE_CURRENT_BINARY_DIR}/ModelicaLibraryConfig_gcc.inc
                ${CMAKE_CURRENT_BINARY_DIR}/ModelicaConfig_gcc.inc
          TYPE INCLUDE)
 
 
 
-
 #####################################################################################################
 # OMCppDataExchange
 set(OMC_SIMRT_CPP_CORE_DATAEXCHANGE_SOURCES DataExchange/SimData.cpp