misc: Use compiler.hh macros when available.

Some places were hand coding __attribute__s when macros in compiler.hh
were available to do that job. Using the macros helps abstract away
compiler specific details and should be used when possible.

Change-Id: I94befebcfde2d673e874e9959588f69781bd9021
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35975
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/gpu-compute/compute_unit.hh

@@ -40,6 +40,7 @@
 #include <vector>
 
 #include "base/callback.hh"
+#include "base/compiler.hh"
 #include "base/statistics.hh"
 #include "base/types.hh"
 #include "config/the_gpu_isa.hh"
@@ -620,8 +621,7 @@ class ComputeUnit : public ClockedObject
     int32_t
     getRefCounter(const uint32_t dispatchId, const uint32_t wgId) const;
 
-    bool
-    sendToLds(GPUDynInstPtr gpuDynInst) __attribute__((warn_unused_result));
+    M5_NODISCARD bool sendToLds(GPUDynInstPtr gpuDynInst);
 
     typedef std::unordered_map<Addr, std::pair<int, int>> pageDataStruct;
     pageDataStruct pageAccesses;