Switch from old-style ASSERT macro to new-style ASSERT_EQ,... macros.
Using new-style macros makes it easier to debug test failures
Fixes: https://github.com/libuv/libuv/issues/2974
This commit adds the support for a custom strtok implementation, which
is reentrant. On some systems strtok_r or strstep is available for that
purpose; however, since these are an extension, it is difficult to
control if it will be available on every supported system.