Backporting patches

This document tries to list all changes that must be made to individual patches when backporting them to earlier branches of the codebase.

This list is incomplete.

OpenMPT 1.28 / libopenmpt 0.4

Replace std::abs by mpt::abs.
Replace std::byte by mpt::byte.
Replace std::clamp by mpt::clamp.
Replace std::data by mpt::data.
Replace std::gcd by mpt::gcd.
Replace std::lcm by mpt::lcm.
Replace std::make_unique by mpt::make_unique.
Replace std::size by mpt::size.
Replace if constexpr by MPT_CONSTANT_IF.
Replace static_assert by MPT_STATIC_ASSERT.
Replace [[nodiscard]] by MPT_NODISCARD.
Replace [[fallthrough]] by MPT_FALLTHROUGH.
Reokace mpt::lock_guard by MPT_LOCK_GUARD.

OpenMPT 1.27 / libopenmpt 0.3

Replace string macros with longer versions:
- U_("foo") --> MPT_USTRING("foo")
- UL_("foo") --> MPT_ULITERAL("foo")
- UC_('x') --> MPT_UCHAR('x')
- P_("foo") --> MPT_PATHSTRING("foo")
- PL_("foo") --> MPT_PATHSTRING_LITERAL("foo")
- PC_('x') --> MPT_PATHSTRING_LITERAL('x') See https://bugs.openmpt.org/view.php?id=1107.