build autotools project with gcov support

usage:

./configure  CFLAGS='-fprofile-arcs -ftest-coverage'
./configure CFLAGS='-fprofile-arcs -ftest-coverage' CXXFLAGS='-fprofile-arcs -ftest-coverage'

cd src
./
gcov 
vim 
...
        -:   25:
        1:   26:if (argv[1][0]=='-') {
    #####:   27:std::cout << "options not supported yet;" << std::endl;
    #####:   28:exit(1);
        -:   29:}
        -:   30:
...

'#####' lines there indicate dead code in this run;
ciphers indicate number of times this peace of code was run.