Fixed some clang-tidy warnings

[gabime]

No description provided.

[vitaut]

Looks good, but could you post the warnings and the repro command?

[gabime]

They come from google-explicit-constructor (google-*) and readability-isolate-declaration (readability-*) checks :

warning: single-argument constructors must be marked explicit to avoid unintentional implicit conversions [google-explicit-constructor]
    constexpr sprintf_specs(basic_format_specs<Char> specs)
              ^
              explicit 

and

warning: multiple declarations in a single statement reduces readability [readability-isolate-declaration]
                auto p = buf.data(), end = p + n;
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[vitaut]

Merged with minor tweaks, thanks.

[gabime]

The pointer specifier was to avoid another clang tidy warning that gets triggered if removed ..

[vitaut]

What's the warning?

[gabime]

readability-qualified-auto

warning: 'auto p' can be declared as 'auto *p' [readability-qualified-auto]
                auto p = buf.data();
                ^~~~~
                auto *
warning: 'auto end' can be declared as 'auto *end' [readability-qualified-auto]
                auto end = p + n;
                ^~~~~
                auto *

[vitaut]

Reapplied the auto change.