Add missing override keyword:

* Enable the `suggest-override` warning for gcc
* Fix all functions that were flagged by that warning

src/test/basics/Buffer_test.cpp

@@ -34,7 +34,7 @@ struct Buffer_test : beast::unit_test::suite
         return b.data() != nullptr;
     }
 
-    void run()
+    void run() override
     {
         std::uint8_t const data[] =
         {

src/test/basics/CheckLibraryVersions_test.cpp

@@ -40,7 +40,7 @@ struct CheckLibraryVersions_test : beast::unit_test::suite
         except ([&]{ checkBoost ("1.54.0"); });
     }
 
-    void run()
+    void run() override
     {
         unexcept ([&]{ checkLibraryVersions(); });
 

src/test/basics/KeyCache_test.cpp

@@ -27,7 +27,7 @@ namespace ripple {
 class KeyCache_test : public beast::unit_test::suite
 {
 public:
-    void run ()
+    void run () override
     {
         TestStopwatch clock;
         clock.set (0);

src/test/basics/PerfLog_test.cpp

@@ -64,7 +64,7 @@ class PerfLog_test : public beast::unit_test::suite
         , j_ (j)
         { }
 
-        ~PerfLogParent()
+        ~PerfLogParent() override
         {
             doStop();
             cleanupPerfLogDir();
@@ -1067,7 +1067,7 @@ public:
         }
     }
 
-    void run()
+    void run() override
     {
         testFileCreation();
         testRPC (WithFile::no);

src/test/basics/RangeSet_test.cpp

@@ -106,7 +106,7 @@ public:
 
     }
     void
-    run()
+    run() override
     {
         testPrevMissing();
         testToString();

src/test/basics/Slice_test.cpp

@@ -27,7 +27,7 @@ namespace test {
 
 struct Slice_test : beast::unit_test::suite
 {
-    void run()
+    void run() override
     {
         std::uint8_t const data[] =
         {

src/test/basics/StringUtilities_test.cpp

@@ -86,7 +86,7 @@ public:
         BEAST_EXPECT(result == "hello");
     }
 
-    void run ()
+    void run () override
     {
         testParseUrl ();
         testUnHex ();

src/test/basics/TaggedCache_test.cpp

@@ -37,7 +37,7 @@ original object.
 class TaggedCache_test : public beast::unit_test::suite
 {
 public:
-    void run ()
+    void run () override
     {
         beast::Journal const j;
 

src/test/basics/base_uint_test.cpp

@@ -51,7 +51,7 @@ struct base_uint_test : beast::unit_test::suite
 {
     using test96 = base_uint<96>;
 
-    void run()
+    void run() override
     {
         // used to verify set insertion (hashing required)
         std::unordered_set<test96, hardened_hash<>> uset;

src/test/basics/contract_test.cpp

@@ -26,7 +26,7 @@ namespace ripple {
 class contract_test : public beast::unit_test::suite
 {
 public:
-    void run ()
+    void run () override
     {
         try
         {

src/test/basics/hardened_hash_test.cpp

@@ -254,7 +254,7 @@ public:
     }
 
     void
-    run ()
+    run () override
     {
         test_user_types();
         test_containers();

src/test/basics/mulDiv_test.cpp

@@ -25,7 +25,7 @@ namespace test {
 
 struct mulDiv_test : beast::unit_test::suite
 {
-    void run()
+    void run() override
     {
         const auto max = std::numeric_limits<std::uint64_t>::max();
         const std::uint64_t max32 = std::numeric_limits<std::uint32_t>::max();

src/test/basics/tagged_integer_test.cpp

@@ -103,7 +103,7 @@ private:
 
 
 public:
-    void run ()
+    void run () override
     {
         using TagInt = tagged_integer<std::int32_t, Tag1>;