Fix a linker error in cctest/test-concurrent-allocation

Bug: v8:10848
Change-Id: Icf014ecd5b0014be258d05aa0f958001f838286b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2381450
Auto-Submit: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69605}

src/codegen/arm64/instructions-arm64.h

@@ -460,7 +460,7 @@ class Instruction {
   static const int ImmPCRelRangeBitwidth = 21;
   static bool IsValidPCRelOffset(ptrdiff_t offset) { return is_int21(offset); }
   void SetPCRelImmTarget(const AssemblerOptions& options, Instruction* target);
-  void SetBranchImmTarget(Instruction* target);
+  V8_EXPORT_PRIVATE void SetBranchImmTarget(Instruction* target);
 };
 
 // Simulator/Debugger debug instructions ---------------------------------------