malloc hooks

[Szabolcs Nagy]

there is some ifdef magic in malloc/hooks.c to
only define malloc_get_state etc if it's needed
for abi compat:

#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_25)

but there is tst-mallocstate.c which uses these
functions unconditionally.

i wonder how that is supposed to work for new
targets (e.g. aarch64 ilp32)