Makefile: modify to use a correct compiler for C about beans

[MartinCupak]

Consequence: the test will not pass, as in the library, there are references to undefined functions

Settle test...
Traceback (most recent call last):
File "try.py", line 8, in
settl = se.settle()
File "/home/martin/src/CIC/Adele/beans/settle/settler.py", line 39, in init
self.libsettle = ct.cdll.LoadLibrary("/usr/local/lib/libsettle.so")
File "/home/martin/miniconda3_py38/envs/beans/lib/python3.8/ctypes/init.py", line 451, in LoadLibrary
return self._dlltype(name)
File "/home/martin/miniconda3_py38/envs/beans/lib/python3.8/ctypes/init.py", line 373, in init
self._handle = _dlopen(self._name, mode)
OSError: /usr/local/lib/libsettle.so: undefined symbol: _Z6matrixllll

[MartinCupak]

Need to add extern "C" { } directive for calling C from C++ (wrap #include headeres)

[MartinCupak]

done as per https://stackoverflow.com/questions/16850992/call-a-c-function-from-c-code