Fix Musl builds

[bivsk]

Describe your PR, what does it fix/add?

Musl does not include the glibc internal type __time_t, causing builds on Musl systems to fail. Use time_t instead.
Fixes #7858

../hyprland-source/src/protocols/PresentationTime.cpp:61:5: error: unknown type name '__time_t'; did you mean 'time_t'?
   61 |     __time_t tv_sec = 0;
      |     ^~~~~~~~
      |     time_t
/usr/include/bits/alltypes.h:85:16: note: 'time_t' declared here
   85 | typedef _Int64 time_t;
      |                ^
../hyprland-source/src/protocols/PresentationTime.cpp:62:16: error: unknown type name '__time_t'; did you mean 'time_t'?
   62 |     if (sizeof(__time_t) > 4)

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

I'm not sure why __time_t is being used here?

[vaxerski]

me neither