[vm] Fix build on gcc 14.2.0.

TEST=local build
Bug: #59617
Change-Id: I4be6ceb489542cee6754a23efdf15401ec91a62b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/397983
Reviewed-by: Alexander Aprelev <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

runtime/vm/compiler/backend/inliner.cc

@@ -1232,7 +1232,7 @@ class CallSiteInliner : public ValueObject {
         constant_arg_count == 0 ? function.optimized_instruction_count() : 0;
     const intptr_t call_site_count =
         constant_arg_count == 0 ? function.optimized_call_site_count() : 0;
-    InliningDecision decision =
+    volatile InliningDecision decision =
         ShouldWeInline(function, instruction_count, call_site_count);
     if (!decision.value) {
       TRACE_INLINING(