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.

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
 */
@@ -409,9 +412,6 @@ 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
   /*
@@ -419,7 +419,7 @@ void my_write_core(int sig)
     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)