gcov: accommodate the execution_count format change in GCC 8.1
gcov: accommodate the execution_count format change in GCC 8.1

The format of gcov's execution_count has been extended to indicate any
unexecuted blocks in a single line, with a following '*':
https://github.com/gcc-mirror/gcc/commit/3cf7fddf54b5160e83236f1b9b3129e2a3a417c6

This confuses cpp-coveralls and leads to a parsing error:

Traceback (most recent call last):
[...]
    coverage.append(int(cov_num))
ValueError: invalid literal for int() with base 10: '2*'

eddyxu/cpp-coveralls,eddyxu/cpp-coveralls