[gdb/testsuite] Reset errcnt in clean_restart

When running test-case gdb.base/readnever.exp without commit 96038148d0e
"[gdb/testsuite] Skip gdb.base/readnever.exp with target board readnow", we
run into an error:
...
ERROR: (eof) GDB never initialized.
testcase gdb/testsuite/gdb.base/readnever.exp completed in 0 seconds
...

If we additionally run test-case gdb.base/realname-expand.exp, we get an
unresolved for the first test:
...
UNRESOLVED: gdb.base/realname-expand.exp: set basenames-may-differ on
...

Using -v we find out that the UNRESOLVED is due the error triggered in the
previous test-case:
...
(gdb) set basenames-may-differ on^M
(gdb) Error/Warning threshold exceeded:  1 0 (max. 1 3)
UNRESOLVED: gdb.base/realname-expand.exp: set basenames-may-differ on
...

So, the error count of one test spills into the next test, even though we do a
clean restart.  That seems like a bad idea.

Fix this by resetting errcnt (as well as warncnt) in clean_restart, such that
we have:
...
Running src/gdb/testsuite/gdb.base/readnever.exp ...
ERROR: (eof) GDB never initialized.
Running src/gdb/testsuite/gdb.base/realname-expand.exp ...
PASS: gdb.base/realname-expand.exp: set basenames-may-differ on
...

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-04-24  Tom de Vries  <tdevries@suse.de>

	* lib/gdb.exp (clean_restart): Reset errcnt and warncnt.

2 files changed, 10 insertions, 2 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index b16366f..7426bdd 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2020-04-24  Tom de Vries  <tdevries@suse.de>
 
+	* lib/gdb.exp (clean_restart): Reset errcnt and warncnt.
+
+2020-04-24  Tom de Vries  <tdevries@suse.de>
+
 	* gdb.dwarf2/dwzbuildid.exp: Add quiet to dwzbuildid-mismatch compile
 	flags.
 
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index cdf96e3..2208f3a 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -6108,6 +6108,7 @@ proc clean_restart { args } {
     global srcdir
     global subdir
     global errcnt
+    global warncnt
 
     if { [llength $args] > 1 } {
 	error "bad number of args: [llength $args]"
@@ -6115,15 +6116,18 @@ proc clean_restart { args } {
 
     gdb_exit
 
+    # This is a clean restart, so reset error and warning count.
+    set errcnt 0
+    set warncnt 0
+
     # We'd like to do:
     #   if { [gdb_start] == -1 } {
     #     return -1
     #   }
     # but gdb_start is a ${tool}_start proc, which doesn't have a defined
     # return value.  So instead, we test for errcnt.
-    set saved_errcnt $errcnt
     gdb_start
-    if { $errcnt > $saved_errcnt } {
+    if { $errcnt > 0 } {
 	return -1
     }