Prevent inlining of zend_compile_expr_inner() to guarantee low stack usage of compilation - #23294

zend_compile_expr_inner() sits in the per-nesting-level recursion cycle of the compiler but normally releases its ~456-byte frame via a tail call before recursing, so a nesting level costs ~155 bytes of stack. Inlined into the cycle, the cost triples (~467 bytes) and the max nesting depth under a 1 MB zend.max_allowed_stack_size drops from ~6700 to ~2200. This actually happened: 07d308a made GCC start inlining it (master shipped ~3 weeks with 3× cost until deeply nested generated code stopped compiling), and fde23df accidentally undid it. Both flips were side effects of unrelated lineno changes — which are planned to return in another form. zend_never_inline makes the cheap state guaranteed instead of accidental; on current master (GCC 13.3 -O2) the compiled output is byte-identical with and without it.

No regression test: one existed while the inlined state was on master and genuinely discriminated there, but since fde23df both builds are identical, so it passes either way on release builds while false-failing on debug (-O0) builds. A test cannot detect an annotation with no observable effect; the attribute and its code comment carry the protection.