Apply clang-tidy to remove empty constructors / destructors

This patch is the result of running
run-clang-tidy -fix -header-filter=.* -checks='-*,modernize-use-equals-default' .

Code style changes have been done on top. The result of this change
leads to the following improvements:

1. Binary size reduction.
* For a -DBUILD_CONFIG=mysql_release build, the binary size is reduced by
  ~400kb.
* A raw -DCMAKE_BUILD_TYPE=Release reduces the binary size by ~1.4kb.

2. Compiler can better understand the intent of the code, thus it leads
   to more optimization possibilities. Additionally it enabled detecting
   unused variables that had an empty default constructor but not marked
   so explicitly.

   Particular change required following this patch in sql/opt_range.cc

   result_keys, an unused template class Bitmap now correctly issues
   unused variable warnings.

   Setting Bitmap template class constructor to default allows the compiler
   to identify that there are no side-effects when instantiating the class.
   Previously the compiler could not issue the warning as it assumed Bitmap
   class (being a template) would not be performing a NO-OP for its default
   constructor. This prevented the "unused variable warning".

1 files changed, 7 insertions, 7 deletions

diff --git a/sql/sql_cache.h b/sql/sql_cache.h
index d89bcda2491..a7c5c62996e 100644
--- a/sql/sql_cache.h
+++ b/sql/sql_cache.h
@@ -91,7 +91,7 @@ typedef my_bool (*qc_engine_callback)(THD *thd, const char *table_key,
 */
 struct Query_cache_block_table
 {
-  Query_cache_block_table() {}                /* Remove gcc warning */
+  Query_cache_block_table() = default;                /* Remove gcc warning */
 
   /**
     This node holds a position in a static table list belonging
@@ -122,7 +122,7 @@ struct Query_cache_block_table
 
 struct Query_cache_block
 {
-  Query_cache_block() {}                      /* Remove gcc warning */
+  Query_cache_block() = default;                      /* Remove gcc warning */
   enum block_type {FREE, QUERY, RESULT, RES_CONT, RES_BEG,
 		   RES_INCOMPLETE, TABLE, INCOMPLETE};
 
@@ -161,7 +161,7 @@ struct Query_cache_query
   uint8 ready;
   ulonglong hit_count;
 
-  Query_cache_query() {}                      /* Remove gcc warning */
+  Query_cache_query() = default;                      /* Remove gcc warning */
   inline void init_n_lock();
   void unlock_n_destroy();
   inline ulonglong found_rows()		   { return limit_found_rows; }
@@ -197,7 +197,7 @@ struct Query_cache_query
 
 struct Query_cache_table
 {
-  Query_cache_table() {}                      /* Remove gcc warning */
+  Query_cache_table() = default;                      /* Remove gcc warning */
   char *tbl;
   uint32 key_len;
   uint8 suffix_len;                          /* For partitioned tables */
@@ -240,7 +240,7 @@ struct Query_cache_table
 
 struct Query_cache_result
 {
-  Query_cache_result() {}                     /* Remove gcc warning */
+  Query_cache_result() = default;                     /* Remove gcc warning */
   Query_cache_block *query;
 
   inline uchar* data()
@@ -266,7 +266,7 @@ extern "C" void query_cache_invalidate_by_MyISAM_filename(const char* filename);
 
 struct Query_cache_memory_bin
 {
-  Query_cache_memory_bin() {}                 /* Remove gcc warning */
+  Query_cache_memory_bin() = default;                 /* Remove gcc warning */
 #ifndef DBUG_OFF
   size_t size;
 #endif
@@ -285,7 +285,7 @@ struct Query_cache_memory_bin
 
 struct Query_cache_memory_bin_step
 {
-  Query_cache_memory_bin_step() {}            /* Remove gcc warning */
+  Query_cache_memory_bin_step() = default;            /* Remove gcc warning */
   size_t size;
   size_t increment;
   size_t idx;