The Rebirth main screen grd_curscreen borrows the memory allocated by
SDL_CreateRGBSurface to store its data. Store the pointer to that
surface inside grd_curscreen and make grd_curscreen responsible for
freeing the surface.
In C++ 20 mode, clang-13 gets confused about how to handle operator==.
Rewrite the test to encourage it to pick the correct version.
```
common/include/gr.h:129:12: error: use of overloaded operator '==' is ambiguous (with operand types 'dcx::grs_main_bitmap *' and 'exact_type<dcx::grs_bitmap>')
if (this == &r)
~~~~ ^ ~~
common/include/pack.h:31:17: note: candidate function (with reversed parameter order)
constexpr bool operator==(const T *rhs) const { return p == rhs; }
^
common/include/gr.h:129:12: note: built-in candidate operator==(struct dcx::grs_bitmap *, struct dcx::grs_bitmap *)
if (this == &r)
```
This field is used in the SDL build for rendering. In the GL build, its
only purpose is for the editor to write it to a PIG file. Change that
one use to compute the value as needed. Move all other references
behind a preprocessor test for !DXX_USE_OGL. This shrinks the size of
grs_bitmap by 1 pointer, since the compiler added padding after
avg_color up to the size of the next aligned pointer.
Bitmaps based on grs_main_bitmap own their data. Bitmaps based on
grs_bitmap do not. Adjust prototypes to prevent initializing a
grs_main_bitmap with data it will not own.
Test DXX_HAVE_CONSTEXPR_UNION_CONSTRUCTOR probes for a bug present in
<=gcc-4.7.x. Rebirth now rejects <=gcc-4.8.x for other reasons, so all
supported gcc versions pass test DXX_HAVE_CONSTEXPR_UNION_CONSTRUCTOR.
Remove the test.
Rename symbol OGL to DXX_USE_OGL to show that it is a DXX
symbol, not one inherited from a library. Move it to dxxsconf.h to
shorten the command line.
This is a mostly automated transform, but the changes to SConstruct were
manual.
git grep -lzw OGL -- '*.h' '*.cpp' | xargs -0 sed -i -e 's/\(\s*#\s*if\)def\s*OGL/\1 DXX_USE_OGL/' -e 's/\(\s*#\s*if\)ndef OGL/\1 !DXX_USE_OGL/' -e 's/\(\s*#\s*if !\?\)defined(OGL)/\1DXX_USE_OGL/'
