Summary:
* `NULL` -> `nullptr`
* `gui` -> Function `getGUI()`
* `pluginFactory` -> Function `getPluginFactory()`
* `assert` (redefinition) -> using `NDEBUG` instead, which standard `assert` respects.
* `powf` (C stdlib symbol clash) -> removed and all expansions replaced with calls to `std::pow`.
* `exp10` (nonstandard function symbol clash) -> removed and all expansions replaced with calls to `std::pow`.
* `PATH_DEV_DSP` -> File-scope QString of identical name and value.
* `VST_SNC_SHM_KEY_FILE` -> constexpr char* with identical name and value.
* `MM_ALLOC` and `MM_FREE` -> Functions with identical name and implementation.
* `INVAL`, `OUTVAL`, etc. for automation nodes -> Functions with identical names and implementations.
* BandLimitedWave.h: All integer constant macros replaced with constexpr ints of same name and value.
* `FAST_RAND_MAX` -> constexpr int of same name and value.
* `QSTR_TO_STDSTR` -> Function with identical name and equivalent implementation.
* `CCONST` -> constexpr function template with identical name and implementation.
* `F_OPEN_UTF8` -> Function with identical name and equivalent implementation.
* `LADSPA_PATH_SEPARATOR` -> constexpr char with identical name and value.
* `UI_CTRL_KEY` -> constexpr char* with identical name and value.
* `ALIGN_SIZE` -> Renamed to `LMMS_ALIGN_SIZE` and converted from a macro to a constexpr size_t.
* `JACK_MIDI_BUFFER_MAX` -> constexpr size_t with identical name and value.
* versioninfo.h: `PLATFORM`, `MACHINE` and `COMPILER_VERSION` -> prefixed with `LMMS_BUILDCONF_` and converted from macros to constexpr char* literals.
* Header guard _OSCILLOSCOPE -> renamed to OSCILLOSCOPE_H
* Header guard _TIME_DISPLAY_WIDGET -> renamed to TIME_DISPLAY_WIDGET_H
* C-style typecasts in DrumSynth.cpp have been replaced with `static_cast`.
* constexpr numerical constants are initialized with assignment notation instead of curly brace intializers.
* In portsmf, `Alg_seq::operator[]` will throw an exception instead of returning null if the operator index is out of range.
Additionally, in many places, global constants that were declared as `const T foo = bar;` were changed from const to constexpr, leaving them const and making them potentially evaluable at compile time.
Some macros that only appeared in single source files and were unused in those files have been removed entirely.
