libctf: low-level list manipulation and helper utilities

libctf: low-level list manipulation and helper utilities

These utilities are a bit of a ragbag of small things needed by more
than one TU: list manipulation, ELF32->64 translators, routines to look
up strings in string tables, dynamically-allocated string appenders, and
routines to set the specialized errno values previously committed in
<ctf-api.h>.

We do still need to dig around in raw ELF symbol tables in places,
because libctf allows the caller to pass in the contents of string and
symbol sections without telling it where they come from, so we cannot
use BFD to get the symbols (BFD reasonably demands the entire file).  So
extract minimal ELF definitions from glibc into a private header named
libctf/elf.h: later, we use those to get symbols.  (The start-of-
copyright range on elf.h reflects this glibc heritage.)

libctf/
	* ctf-util.c: New file.
	* elf.h: Likewise.
	* ctf-impl.h: Include it, and add declarations.