MDEV-30573 Server doesn't build with GCOV by GCC 11+

__gcov_flush was never an external symbol in the documentation.

It was removed in gcc-11. The correct function to use is __gcov_dump
which is defined in the gcov.h header.

Author: grooverdan

dbug/dbug.c

@@ -86,7 +86,7 @@
 #include <m_string.h>
 #include <errno.h>
 #ifdef HAVE_gcov
-extern void __gcov_flush();
+#include <gcov.h>
 #endif
 
 #ifndef DBUG_OFF
@@ -2212,7 +2212,7 @@ void _db_suicide_()
   fprintf(stderr, "SIGKILL myself\n");
   fflush(stderr);
 #ifdef HAVE_gcov
-  __gcov_flush();
+  __gcov_dump();
 #endif
 
   retval= kill(getpid(), SIGKILL);
@@ -2262,7 +2262,7 @@ my_bool _db_my_assert(const char *file, int line, const char *msg)
     fprintf(stderr, "%s:%d: assert: %s\n", file, line, msg);
     fflush(stderr);
 #ifdef HAVE_gcov
-    __gcov_flush();
+    __gcov_dump();
 #endif
   }
   return a;

mysys/stacktrace.c

@@ -34,6 +34,9 @@
 #include <execinfo.h>
 #endif
 
+#ifdef HAVE_gcov
+#include <gcov.h>
+#endif
 /**
    Default handler for printing stacktrace
 */
@@ -409,17 +412,14 @@ void my_print_stacktrace(uchar* stack_bottom, ulong thread_stack,
 /* Produce a core for the thread */
 void my_write_core(int sig)
 {
-#ifdef HAVE_gcov
-  extern void __gcov_flush(void);
-#endif
   signal(sig, SIG_DFL);
 #ifdef HAVE_gcov
   /*
     For GCOV build, crashing will prevent the writing of code coverage
     information from this process, causing gcov output to be incomplete.
     So we force the writing of coverage information here before terminating.
   */
-  __gcov_flush();
+  __gcov_dump();
 #endif
   pthread_kill(pthread_self(), sig);
 #if defined(P_MYID) && !defined(SCO)