Handle recursive internal problem in gdb_internal_error_resync

I came across this problem when testing gdb.base/gdb-sigterm.exp
on a machine with a pre-release version of glib-2.34 installed:

A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) Recursive internal problem.
FAIL: gdb.base/gdb-sigterm.exp: expect eof #0 (GDB internal error)
Resyncing due to internal error.
ERROR: : spawn id exp11 not open
    while executing
"expect {
-i exp11 -timeout 10
	    -re "Quit this debugging session\\? \\(y or n\\) $" {
		send_gdb "n\n" answer
		incr count
	    }
	    -re "Create..."
    ("uplevel" body line 1)
    invoked from within
"uplevel $body" NONE : spawn id exp11 not open
ERROR: Could not resync from internal error (timeout)
gdb.base/gdb-sigterm.exp: expect eof #0: stepped 9 times
UNRESOLVED: gdb.base/gdb-sigterm.exp: 50 SIGTERM passes

I don't have a problem with the latter ERROR nor the UNRESOLVED
messages.  However the first ERROR regarding the exp11 spawn id
not being open is not especially useful.

This commit handles the "Recursive internal problem" case, avoiding
the problematic ERROR shown above.

With this commit in place, the log messages look like this instead:

A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) Recursive internal problem.
FAIL: gdb.base/gdb-sigterm.exp: expect eof riscvarchive#15 (GDB internal error)
Resyncing due to internal error.
ERROR: Could not resync from internal error (recursive internal problem)
gdb.base/gdb-sigterm.exp: expect eof riscvarchive#15: stepped 12 times
UNRESOLVED: gdb.base/gdb-sigterm.exp: 50 SIGTERM passes

gdb/testsuite/ChangeLog:

	* lib/gdb.exp (gdb_internal_error_resync): Handle "Recursive
	internal problem".

gdb/testsuite/lib/gdb.exp

@@ -770,6 +770,10 @@ proc gdb_internal_error_resync {} {
     set count 0
     while {$count < 10} {
 	gdb_expect {
+	    -re "Recursive internal problem\\." {
+		perror "Could not resync from internal error (recursive internal problem)"
+		return 0
+	    }
 	    -re "Quit this debugging session\\? \\(y or n\\) $" {
 		send_gdb "n\n" answer
 		incr count