Fix custom printf/malloc

[ZERICO2005]

• Fixes cedev-obj only searches lto.s #736
• reimplemented ALLOCATOR = CUSTOM
• fixes user provided custom printf

The test for std::terminate was added to make sure that sprintf (used by std::terminate) is linked even if no functions from libnanoprintf.a are directly referenced by lto.s.

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

int main(void) {
    os_ClrHome();
    os_PutStrFull("before std::terminate");
    while (!os_GetCSC());

    std::terminate();
}

---

To define a custom malloc/free/realloc, the user must set ALLOCATOR = CUSTOM in the makefile, then they just have to define malloc in one of two ways:

// it is recommended but not strictly necessary to #include <stdlib.h>
#include <stdlib.h>
void *malloc(size_t size) {
    /* code */
}

	.global	_malloc
	.type	_malloc, @function
_malloc:
	; code
	ret

This does remove support for _custom_malloc/_custom_free/_custom_realloc, but the user can fix it by doing:

	.global	_malloc
	.type	_malloc, @function
_malloc:
	jp _custom_malloc
	.extern _custom_malloc