Fix compilation with Google Benchmark >= 1.9.2

Bug: https://bugs.gentoo.org/960483
--- a/benchmarks/bench_utils/custom_reporter.hpp
+++ b/benchmarks/bench_utils/custom_reporter.hpp
@@ -88,6 +88,21 @@ static std::string FormatString(const char* msg, ...)
     return tmp;
 }
 
+// 'run.memory_result' is a pointer (Google Benchmark < 1.9.2).
+inline const benchmark::MemoryManager::Result*
+GetMemoryResultPtr(const benchmark::MemoryManager::Result* p) {
+    return p;
+}
+
+// 'run.memory_result' is an object (Google Benchmark >= 1.9.2).
+inline const benchmark::MemoryManager::Result*
+GetMemoryResultPtr(const benchmark::MemoryManager::Result& v) {
+    if (v.memory_iterations > 0) {
+        return &v;
+    }
+    return nullptr;
+}
+
 std::string get_complexity(const benchmark::BigO& complexity)
 {
     switch(complexity)
@@ -658,9 +673,10 @@ class CustomJSONReporter : public benchmark::JSONReporter
             }
         }
 
-        if (run.memory_result)
+        const benchmark::MemoryManager::Result* mem_result = GetMemoryResultPtr(run.memory_result);
+        if (mem_result)
         {
-            const benchmark::MemoryManager::Result memory_result = *run.memory_result;
+            const benchmark::MemoryManager::Result& memory_result = *mem_result;
             output_format("allocs_per_iter", run.allocs_per_iter);
             output_format("max_bytes_used", memory_result.max_bytes_used);