assert: Do not use stderr in libc-internal assert

Redirect internal assertion failures to __libc_assert_fail, based on
based on __libc_message, which writes directly to STDERR_FILENO
and calls abort.  Also disable message translation and reword the
error message slightly (adjusting stdlib/tst-bz20544 accordingly).

As a result of these changes, malloc no longer needs its own
redefinition of __assert_fail.

__libc_assert_fail needs to be stubbed out during rtld dependency
analysis because the rtld rebuilds turn __libc_assert_fail into
__assert_fail, which is unconditionally provided by elf/dl-minimal.c.

This change is not possible for the public assert macro and its
__assert_fail function because POSIX requires that the diagnostic
is written to stderr.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

assert/assert.c

@@ -101,4 +101,3 @@ __assert_fail (const char *assertion, const char *file, unsigned int line,
   __assert_fail_base (_("%s%s%s:%u: %s%sAssertion `%s' failed.\n%n"),
 		      assertion, file, line, function);
 }
-hidden_def(__assert_fail)