AOT: integer subtraction overflow promotes to float (#32422)

[PurHur]

Summary

• Native-long - used LLVM sub nsw and wrapped (PHP_INT_MIN - 1 → int(PHP_INT_MAX)). Zend sub_function / fast_long_sub_function promotes to double (Zend/zend_operators.h).
• Extends #31964 JitLongArithOverflow to TYPE_MINUS (portable sign-bit overflow: operand signs differ and wrapping result sign differs from op1). Const-fold uses PHP native $a - $b. Folded integer constants use int64 (constantFromInteger(..., 'long') is not a mapped LLVM type).
• No new runtime/*.c.

Closes #32422

Test plan

• ./script/docker-exec.sh -- bash -lc 'export PHP_COMPILER_HELPER_RUNTIME_O=0 PHP_COMPILER_HELPER_RUNTIME_CACHE_DIR=/tmp/phpc-32422-aot-smoke; mkdir -p /tmp/phpc-32422-aot-smoke; ./script/aot-smoke.sh'

  aot-smoke: 8 passed, 0 failed
  

• ./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/issue_int_sub_overflow.php'

  float(-9.223372036854776E+18)
  float(-9.223372036854776E+18)
  float(9.223372036854776E+18)
  int(7)
  

• ./script/docker-exec.sh -- bash -lc 'export PHP_COMPILER_HELPER_RUNTIME_O=0 PHP_COMPILER_HELPER_RUNTIME_CACHE_DIR=/tmp/phpc-32422-repro PHP_COMPILER_LLVM_ASSERT=1; mkdir -p /tmp/phpc-32422-repro; php bin/compile.php -o /tmp/iso.bin test/repro/issue_int_sub_overflow.php && /tmp/iso.bin'
  same four lines as VM / Zend
• ./script/phpunit.sh --filter 'IntSubOverflowPromote32422|IntArithOverflowPromote31964'

  OK (4 tests, 14 assertions)
  

Not covered: full ci-local.sh / north-star5-verify --strict / compliance suites.

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