Fix libc++ error: no matching function for call to object of type 'const std::less<void>'.
libstdc++ compiles due too loose standard following, allowing to compare some structs without a comparator.
Upstream bug: https://github.com/ROCm/rocm-systems/issues/3307
--- a/runtime/hsa-runtime/core/inc/amd_gpu_agent.h
+++ b/runtime/hsa-runtime/core/inc/amd_gpu_agent.h
@@ -575,8 +575,14 @@ class GpuAgent : public GpuAgentInt {
   // @brief Current short duration scratch memory size.
   size_t scratch_used_large_;
 
+  struct HsaSignalLess {
+    bool operator()(const hsa_signal_t& lhs, const hsa_signal_t& rhs) const {
+      return lhs.handle < rhs.handle;
+    }
+  };
+
   // @brief Notifications for scratch release.
-  std::map<hsa_signal_t, hsa_signal_value_t> scratch_notifiers_;
+  std::map<hsa_signal_t, hsa_signal_value_t, HsaSignalLess> scratch_notifiers_;
 
   // @brief Default scratch size per queue.
   size_t queue_scratch_len_;