Try to regain gcov for tests which panic.

bin/varnishd/cache/cache_panic.c

@@ -63,6 +63,10 @@
  *
  */
 
+#ifdef GCOVING
+    int __llvm_profile_write_file(void);
+#endif
+
 static struct vsb pan_vsb_storage, *pan_vsb;
 static pthread_mutex_t panicstr_mtx;
 
@@ -811,6 +815,9 @@ pan_ic(const char *func, const char *file, int line, const char *cond,
 	VSB_cat(pan_vsb, "\n");
 	VSB_putc(pan_vsb, '\0');	/* NUL termination */
 
+#ifdef GCOVING
+	__llvm_profile_write_file();
+#endif
 	abort();
 }
 

bin/varnishd/mgt/mgt_cli.c

@@ -63,6 +63,10 @@ static const struct cli_cmd_desc *cmds[] = {
 #include "tbl/cli_cmds.h"
 };
 
+#ifdef GCOVING
+    int __llvm_profile_write_file(void);
+#endif
+
 static const int ncmds = sizeof cmds / sizeof cmds[0];
 
 static int		cli_i = -1, cli_o = -1;
@@ -108,6 +112,9 @@ mcf_panic(struct cli *cli, const char * const *av, void *priv)
 	(void)cli;
 	(void)av;
 	(void)priv;
+#ifdef GCOVING
+	__llvm_profile_write_file();
+#endif
 	AZ(strcmp("", "You asked for it"));
 	/* NOTREACHED */
 	abort();