IO::Handle: clear the error on both input and output streams

Similarly to GH Perl#6799 clearerr() only cleared the error status
of the input stream, so clear both.

Author: tonycoz

dist/IO/IO.xs

@@ -410,13 +410,21 @@ ferror(handle)
 
 int
 clearerr(handle)
-	InputStream	handle
+	SV *	handle
+    PREINIT:
+        IO *io = sv_2io(handle);
+        InputStream in = IoIFP(io);
+        OutputStream out = IoOFP(io);
     CODE:
 	if (handle) {
 #ifdef PerlIO
-	    PerlIO_clearerr(handle);
+	    PerlIO_clearerr(in);
+            if (in != out)
+                PerlIO_clearerr(out);
 #else
-	    clearerr(handle);
+	    clearerr(in);
+            if (in != out)
+                clearerr(out);
 #endif
 	    RETVAL = 0;
 	}

dist/IO/t/io_xs.t

@@ -11,7 +11,7 @@ BEGIN {
     }
 }
 
-use Test::More tests => 7;
+use Test::More tests => 8;
 use IO::File;
 use IO::Seekable;
 
@@ -58,12 +58,14 @@ SKIP: {
     # This isn't really a Linux/BSD specific test, but /dev/full is (I
     # hope) reasonably well defined on these.  Patches welcome if your platform
     # also supports it (or something like it)
-    skip "no /dev/full or not a /dev/full platform", 2
+    skip "no /dev/full or not a /dev/full platform", 3
       unless $^O =~ /^(linux|netbsd|freebsd)$/ && -c "/dev/full";
     open my $fh, ">", "/dev/full"
-      or skip "Could not open /dev/full: $!", 2;
+      or skip "Could not open /dev/full: $!", 3;
     $fh->print("a" x 1024);
     ok(!$fh->flush, "should fail to flush");
     ok($fh->error, "stream should be in error");
+    $fh->clearerr;
+    ok(!$fh->error, "check clearerr removed the error");
     close $fh; # silently ignore the error
 }