Fix compiling with a cleaner solution

As stated
[here](https://docs.python.org/3/whatsnew/3.8.html#debug-build-uses-the-same-abi-as-release-build),
starting from Python 3.8 `python3-config` has to be called with
`--embed` in order to link to python itself.
To be backwards compatible it should always be tried with `--embed` and
when it fails retrying without.
This is the logic implemented.

CMakeLists.txt

@@ -22,7 +22,7 @@ find_package(Boost REQUIRED COMPONENTS program_options)
 include_directories(${Boost_INCLUDE_DIRS})
 
 if(PY3)
-    set(Python_ADDITIONAL_VERSIONS 3.7 3.6 3.5 3.4 3.3)
+    set(Python_ADDITIONAL_VERSIONS 3.8 3.7 3.6 3.5 3.4 3.3)
     find_package(PythonInterp 3 REQUIRED)
 else()
     set(Python_ADDITIONAL_VERSIONS 2.7 2.6)
@@ -46,7 +46,7 @@ set_target_properties(cpsm_core PROPERTIES COMPILE_FLAGS "-fPIC")
 add_library(cpsm_py SHARED src/ctrlp_util.cc src/python_extension.cc)
 target_link_libraries(cpsm_py cpsm_core)
 set_target_properties(cpsm_py PROPERTIES COMPILE_FLAGS ${PYTHON_COMPILE_FLAGS})
-set_target_properties(cpsm_py PROPERTIES LINK_FLAGS "${PYTHON_LINK_FLAGS} -lpython3.8")
+set_target_properties(cpsm_py PROPERTIES LINK_FLAGS ${PYTHON_LINK_FLAGS})
 set_target_properties(cpsm_py PROPERTIES PREFIX "")
 if(APPLE)
   set_target_properties(cpsm_py PROPERTIES SUFFIX ".so")

cmake/FindPythonConfig.cmake

@@ -18,7 +18,11 @@ find_package(PythonInterp)
 if(PYTHONINTERP_FOUND)
   set(_Python_config "${PYTHON_EXECUTABLE}-config")
   execute_process(COMMAND ${_Python_config} "--includes" OUTPUT_VARIABLE PYTHON_COMPILE_FLAGS OUTPUT_STRIP_TRAILING_WHITESPACE)
-  execute_process(COMMAND ${_Python_config} "--ldflags" OUTPUT_VARIABLE PYTHON_LINK_FLAGS OUTPUT_STRIP_TRAILING_WHITESPACE)
+  execute_process(COMMAND ${_Python_config} "--ldflags" "--embed" OUTPUT_VARIABLE PYTHON_LINK_FLAGS OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_VARIABLE PYTHON_EMBED_FAILED)
+  if(PYTHON_EMBED_FAILED)
+    message(STATUS "PythonConfig could not embed Python. (Fine for < Python 3.8)")
+    execute_process(COMMAND ${_Python_config} "--ldflags" OUTPUT_VARIABLE PYTHON_LINK_FLAGS OUTPUT_STRIP_TRAILING_WHITESPACE)
+  endif(PYTHON_EMBED_FAILED)
   set(_Python_config_message "${PYTHON_COMPILE_FLAGS}; ${PYTHON_LINK_FLAGS}")
   unset(_Python_config)
 else(PYTHONINTERP_FOUND)