None of the functions in these files come from ctype.h

Also changed one instance of isdigit to the C++ variant.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Debian Stable (Buster) has GCC 8 and Ubuntu LTS (18.04) has GCC 7.

This will unlock a lot of C++17 features like `std::string_view`.

Introduced in C++17. It replaces gcc's warn_unused_result.

Found with modernize-use-nodiscard.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Fixes assertion failure.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/774

Fixes access to uninitialized memory (`remaining_bytes` isn't
initialized until Ready() is called) and fixes spurious
`getfingerprint` failures.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/781

Similar to commits e8f2f980 and
ff1ff1e5

Closes https://github.com/MusicPlayerDaemon/MPD/issues/783

Travis has changed the canonical name for this a while ago.

(Now really.  The last commit for this was empty.)

Aparently, libcdio sometimes returns empty filenames, causing MPD
crashes.  This shouldn't really happen, and I consider this a libcdio
bug - but if it happens, people blame MPD, so let's add a check.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/776

Merge some duplicate code in a central library.

Workaround for Travis failures as described in
 https://travis-ci.community/t/macos-build-fails-because-of-homebrew-bundle-unknown-command/7296/18

Travis has changed the canonical name for this a while ago.

Fixes
../src/time/ISO8601.cxx:67:24: error: use of undeclared identifier 'strtoul'
        unsigned long value = strtoul(s, &endptr, 10);
                              ^
../src/time/ISO8601.cxx:77:14: error: use of undeclared identifier 'strtoul'
                        minutes = strtoul(s, &endptr, 10);
                                  ^

on NetBSD with clang 9.0.0.

Using libgme 0.6.2 on macOS, it appears that gme_info_t strings can be
empty, which creates weird track titles: (001/050)

This adds an additional check for an empty string.

Found with performance-move-const-arg
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Move the existing systemd sections over there.

Found with modernize-use-using
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with hicpp-use-emplace
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with modernize-use-equals-default
Signed-off-by: Rosen Penev <rosenp@gmail.com>