Replace __gcov_flush with __gcov_dump

__gcov_flush was a private function and was removed from later GCC
versions (at least from 11.2.0, possibly earlier). Replace with the
documented public __gcov_dump.

include/verilated.cpp

@@ -2809,7 +2809,7 @@ void Verilated::runFlushCallbacks() VL_MT_SAFE {
     // When running internal code coverage (gcc --coverage, as opposed to
     // verilator --coverage), dump coverage data to properly cover failing
     // tests.
-    VL_GCOV_FLUSH();
+    VL_GCOV_DUMP();
 }
 
 void Verilated::addExitCb(VoidPCb cb, void* datap) VL_MT_SAFE {

include/verilatedos.h

@@ -255,14 +255,11 @@
 // Internal coverage
 
 #ifdef VL_GCOV
-extern "C" {
-void __gcov_flush();  // gcc sources gcc/gcov-io.h has the prototype
-}
-// Flush internal code coverage data before e.g. std::abort()
-# define VL_GCOV_FLUSH() \
-    __gcov_flush()
+extern "C" void __gcov_dump();
+// Dump internal code coverage data before e.g. std::abort()
+# define VL_GCOV_DUMP() __gcov_dump()
 #else
-# define VL_GCOV_FLUSH()
+# define VL_GCOV_DUMP()
 #endif
 
 //=========================================================================

src/V3Error.cpp

@@ -167,7 +167,7 @@ void V3Error::vlAbortOrExit() {
 }
 
 void V3Error::vlAbort() {
-    VL_GCOV_FLUSH();
+    VL_GCOV_DUMP();
     std::abort();
 }