analyzer: avoid relying on system <assert.h> in testsuite (PR 93367)

analyzer: avoid relying on system <assert.h> in testsuite (PR 93367)

PR analyzer/93367 reports a testsuite failure in abort.c on
hppa64-hp-hpux11.11 when detecting if the analyzer "knows" that the
condition holds after the assert.

The root cause is that the assertion failure function in that
configuration's <assert.h> is not marked with
__attribute__ ((__noreturn__)).

This patch reworks the test to avoid <assert.h> in favor of a custom
implementation of assert, so that the test demonstrates the idea without
relying on properties of <assert.h>.

gcc/testsuite/ChangeLog:
	PR analyzer/93367
	* gcc.dg/analyzer/abort.c: Remove include of <assert.h>.
	Replace use of assert with a custom assertion implementation.