[NFC][sanitizer] Add a few consts

Depends on D111609.

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D111610

compiler-rt/lib/sanitizer_common/sanitizer_stackdepot.cpp

@@ -69,8 +69,8 @@ struct StackDepotNode {
 
 COMPILER_CHECK(StackDepotNode::kMaxUseCount >= (u32)kStackDepotMaxUseCount);
 
-u32 StackDepotHandle::id() { return node_->id; }
-int StackDepotHandle::use_count() {
+u32 StackDepotHandle::id() const { return node_->id; }
+int StackDepotHandle::use_count() const {
   return atomic_load(&node_->tag_and_use_count, memory_order_relaxed) &
          StackDepotNode::kUseCountMask;
 }

compiler-rt/lib/sanitizer_common/sanitizer_stackdepot.h

@@ -25,9 +25,9 @@ struct StackDepotHandle {
   StackDepotNode *node_;
   StackDepotHandle() : node_(nullptr) {}
   explicit StackDepotHandle(StackDepotNode *node) : node_(node) {}
-  bool valid() { return node_; }
-  u32 id();
-  int use_count();
+  bool valid() const { return node_; }
+  u32 id() const;
+  int use_count() const;
   void inc_use_count_unsafe();
 };