By writing the fxc and dxc output to a temporary file and then
converting that temporary file to the desired filename, we avoid
the incompatible semantics of sed -i on GNU systems (sed -i does not
create a backup filename, and does not take an argument unless it is
"bundled") and macOS (sed -i requires an argument, possibly empty).
Resolves: https://github.com/libsdl-org/SDL/issues/10878
Signed-off-by: Simon McVittie <smcv@debian.org>
We require stdbool.h in the build environment, so we might as well use the plain bool type.
If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;
We want `$USE_FXC` to default to the result of evaluating the variable
`$HAVE_FXC`, not the literal string `HAVE_FXC`, and the same for dxc.
Signed-off-by: Simon McVittie <smcv@debian.org>
