Which means that reduz' beloved style which we all became used to
will now be changed automatically to remove the first empty line.
This makes us lean closer to 1TBS (the one true brace style) instead
of hybridating it with some Allman-inspired spacing.
There's still the case of braces around single-statement blocks that
needs to be addressed (but clang-format can't help with that, but
clang-tidy may if we agree about it).
Part of #33027.
Namely:
```
modules/basis_universal/register_types.cpp: In function 'Ref<Image> basis_universal_unpacker(const Vector<unsigned char>&)':
modules/basis_universal/register_types.cpp:266:15: warning: 'imgfmt' may be used uninitialized in this function [-Wmaybe-uninitialized]
266 | image->create(info.m_width, info.m_height, info.m_total_levels > 1, imgfmt, gpudata);
| ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
modules/basis_universal/register_types.cpp:255:39: warning: 'format' may be used uninitialized in this function [-Wmaybe-uninitialized]
255 | bool ret = tr.transcode_image_level(ptr, size, 0, i, dst + ofs, level.m_total_blocks - i, format);
| ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
```
servers/visual_server.cpp: In member function 'Error VisualServer::_surface_set_data(Array, uint32_t, uint32_t*, uint32_t, Vector<unsigned char>&, int, Vector<unsigned char>&, int, AABB&, Vector<AABB>&)':
servers/visual_server.cpp:636:15: warning: 'iw' may be used uninitialized in this function [-Wmaybe-uninitialized]
636 | copymem(&iw[i * 2], &v, 2);
| ^
```
```
core/image.cpp: In member function 'Error Image::generate_mipmap_roughness(Image::RoughnessChannel, const Ref<Image>&)':
core/image.cpp:1683:11: warning: 'roughness' may be used uninitialized in this function [-Wmaybe-uninitialized]
1683 | float roughness;
| ^~~~~~~~~
```
Fix -Wunused-variable, -Wunused-but-set-variable and -Wswitch warnings
raised by GCC 8 and 9.
Fix -Wunused-function, -Wunused-private-field and
-Wtautological-constant-out-of-range-compare raised by Clang.
Fix MSVC 2019 warning C4804 (unsafe use of type 'bool' in comparison
operation).
GCC -Wcpp warnings/Clang -W#warnings (`#warning`) are no longer raising
errors and will thus not abort compilation with `werror=yes`.
Treat glslang headers are system headers to avoid raising warnings.
Re-enables us to build with `werror=yes` on Linux and macOS, thus
catching warnings that would be introduced by new code.
Fixes#36132.