Correctly define ABSL_UNREACHABLE when Abseil Hardened Fast is enabled

Currently, when Abseil Hardened Fast is set and NDEBUG is set,
ABSL_UNREACHABLE performs undefined behavior, as the assert is a no-op
and the various ABSL_UNREACHABLE_IMPLs can in fact be reached, violating
assumptions we have told the compiler to make.

PiperOrigin-RevId: 866148746
Change-Id: I4fcad9681d167c40be082521c3bebd9fc27109dc

absl/base/optimization.h

diff --git a/absl/base/optimization.h b/absl/base/optimization.h
index 04678c4..b561128 100644
--- a/absl/base/optimization.h
+++ b/absl/base/optimization.h
@@ -222,7 +222,7 @@
 
 // `ABSL_UNREACHABLE()` is an unreachable statement.  A program which reaches
 // one has undefined behavior, and the compiler may optimize accordingly.
-#if ABSL_OPTION_HARDENED == 1 && defined(NDEBUG)
+#if (ABSL_OPTION_HARDENED == 1 || ABSL_OPTION_HARDENED == 2) && defined(NDEBUG)
 // Abort in hardened mode to avoid dangerous undefined behavior.
 #define ABSL_UNREACHABLE()                \
   do {                                    \