Fix atexit/on_exit/_Exit

[ZERICO2005]

Fixes #734

• Fixed return values from on_exit/atexit
• Fixed the exit-status passed to on_exit functions via returning from main and via exit
• Re-implemented C99 _Exit
• Adds HAS_EXIT and HAS_C99__EXIT which will only include exit() and _Exit() in crt0.S if the functions are needed (similar to HAS_ABORT)

There are other issues that this PR does not fix, such as HAS_ABORT being 0 when abort is indirectly linked. Currently this PR just patches it so HAS_ABORT and HAS_EXIT are always set to 1 to prevent linker errors for the user. More here: #736

[ZERICO2005]

These corrections are still not enough actually, this test program fails to link

#include <ti/screen.h>
#include <ti/getcsc.h>
#include <ti/sprintf.h>

#include <errno.h>
#include <exception>

extern "C" int main(void) {
    errno = 0;
    os_ClrHome();

    char buf[sizeof("errno: -8388608\n")];
    boot_sprintf(buf, "errno: %d\n", errno);
    os_PutStrFull(buf);

    while (!os_GetCSC());

    std::terminate();
}

zerico@DESKTOP-7OMIH9B:~/programming/toolchain$ make -C test/crt/terminate
make: Entering directory '/home/zerico/programming/toolchain/test/crt/terminate'
[cc] src/main.cpp
[lto] obj/lto.bc
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: warning: indcallhl.o: missing .note.GNU-stack section implies executable stack
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
[linking] bin/DEMO.obj
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: warning: obj/DEMO.o: requires executable stack (because the .note.GNU-stack section is executable)
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: obj/DEMO.o: in function `___abort_message':
(.text.___abort_message+0x13): undefined reference to `_sprintf'
make: *** [/home/zerico/programming/toolchain/CEdev/meta/makefile.mk:377: bin/DEMO.obj] Error 1
make: Leaving directory '/home/zerico/programming/toolchain/test/crt/terminate'
zerico@DESKTOP-7OMIH9B:~/programming/toolchain$ 

[ZERICO2005]

not sure why those tests failed. It compiles fine on clang 19

zerico@DESKTOP-7OMIH9B:~/programming/toolchain$ make -C test/standalone/custom_lib clean
make: Entering directory '/home/zerico/programming/toolchain/test/standalone/custom_lib'
Removed built binaries and objects.
make: Leaving directory '/home/zerico/programming/toolchain/test/standalone/custom_lib'
zerico@DESKTOP-7OMIH9B:~/programming/toolchain$ make -C test/standalone/custom_lib
make: Entering directory '/home/zerico/programming/toolchain/test/standalone/custom_lib'
[cc] src/custom_malloc.c
[cc] src/custom_sprintf.c
[cc] src/main.c
[lto] obj/lto.bc
[as] src/custom_free.s
[convimg] description
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: warning: imulu.o: missing .note.GNU-stack section implies executable stack
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
[linking] bin/DEMO.obj
/home/zerico/programming/toolchain/CEdev/binutils/bin/z80-none-elf-ld: warning: obj/DEMO.o: requires executable stack (because the .note.GNU-stack section is executable)
[success] bin/DEMO.8xp, 1060 bytes.
make: Leaving directory '/home/zerico/programming/toolchain/test/standalone/custom_lib'
zerico@DESKTOP-7OMIH9B:~/programming/toolchain$