runtests: handle interrupted reads from IPC pipes

These can be interrupted by signals, especially SIGINT to shut down, and
must be restarted so the IPC call arrives correctly. If the read just
returns an error instead, the IPC calling state will go out of sync and
a proper shutdown won't happen.

Ref: curl#10818

Author: dfandrich

tests/runner.pm

@@ -1203,14 +1203,17 @@ sub controlleripccall {
 # Called by controller
 sub runnerar {
     my ($runnerid) = @_;
+    my $err;
     my $datalen;
-    if (sysread($controllerr{$runnerid}, $datalen, 4) <= 0) {
-        die "error in runnerar\n";
+    while(! defined ($err = sysread($controllerr{$runnerid}, $datalen, 4)) || $err <= 0) {
+        $!{EINTR} || die "error in runnerar: $!\n";
+        # system call was interrupted, probably by ^C; restart it so we stay in sync
     }
     my $len=unpack("L", $datalen);
     my $buf;
-    if (sysread($controllerr{$runnerid}, $buf, $len) <= 0) {
-        die "error in runnerar\n";
+    while(! defined ($err = sysread($controllerr{$runnerid}, $buf, $len)) || $err <= 0) {
+        $!{EINTR} || die "error in runnerar: $!\n";
+        # system call was interrupted, probably by ^C; restart it so we stay in sync
     }
 
     # Decode response values
@@ -1259,14 +1262,17 @@ sub runnerar_ready {
 # The IPC is read from the $runnerr pipe and the response is
 # written to the $runnerw pipe
 sub ipcrecv {
+    my $err;
     my $datalen;
-    if (sysread($runnerr, $datalen, 4) <= 0) {
-        die "error in ipcrecv\n";
+    while(! defined ($err = sysread($runnerr, $datalen, 4)) || $err <= 0) {
+        $!{EINTR} || die "error in ipcrecv: $!\n";
+        # system call was interrupted, probably by ^C; restart it so we stay in sync
     }
     my $len=unpack("L", $datalen);
     my $buf;
-    if (sysread($runnerr, $buf, $len) <= 0) {
-        die "error in ipcrecv\n";
+    while(! defined ($err = sysread($runnerr, $buf, $len)) || $err <= 0) {
+        $!{EINTR} || die "error in ipcrecv: $!\n";
+        # system call was interrupted, probably by ^C; restart it so we stay in sync
     }
 
     # Decode the function name and arguments