Prevent cross-module inlining of stack unwinder wrappers that adjust skip counts.

`absl::DefaultStackUnwinder`, `CurrentStackTrace`, and `SavedStackTrace::CreateCurrent` increment `skip_count` assuming they occupy their own stack frame on the call stack, but were missing `ABSL_ATTRIBUTE_NOINLINE`. When LLVM commit `fc1afa6edce98a973ce2ce969c589da4f3aee975` enabled ThinLTO inlining of imported CFI jump table functions across translation units, these wrappers were inlined into their callers, causing stack unwinding to skip an extra caller frame.

Add `ABSL_ATTRIBUTE_NOINLINE` (and `ABSL_ATTRIBUTE_NO_TAIL_CALL` / `ABSL_BLOCK_TAIL_CALL_OPTIMIZATION()`) to ensure their stack frames are preserved when calculating `skip_count`.

PiperOrigin-RevId: 983379727
Change-Id: Ie6bdab705ebd1bf5c9acc1cc875e5ec535a84730

absl/debugging/stacktrace.cc

diff --git a/absl/debugging/stacktrace.cc b/absl/debugging/stacktrace.cc
index 9689337..6dc366c 100644
--- a/absl/debugging/stacktrace.cc
+++ b/absl/debugging/stacktrace.cc
@@ -161,8 +161,14 @@
   custom.store(w, std::memory_order_release);
 }
 
-int DefaultStackUnwinder(void** pcs, int* sizes, int depth, int skip,
-                         const void* uc, int* min_dropped_frames) {
+// As of LLVM commit go/compilers/fc1afa6edce98a973ce2ce969c589da4f3aee975,
+// CFI functions are inlinable in the ThinLTO backend. As a result, these
+// wrappers were inlined into their callers, causing stack unwinding to skip an
+// extra caller frame. Prevent inlining to ensure their stack frames are
+// preserved when calculating `skip_count`.
+ABSL_ATTRIBUTE_NOINLINE ABSL_ATTRIBUTE_NO_TAIL_CALL int DefaultStackUnwinder(
+    void** pcs, int* sizes, int depth, int skip, const void* uc,
+    int* min_dropped_frames) {
   skip++;  // For this function
   decltype(&UnwindImpl<false, false>) f;
   if (sizes == nullptr) {