build: fix flags for ngtcp2 on IBM i

PR-URL: #60073
Backport-PR-URL: #64675
Reviewed-By: Richard Lau <richard.lau@ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Abdirahim Musse <abdirahim.musse@ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: sravani1510

deps/ngtcp2/ngtcp2.gyp

@@ -274,7 +274,7 @@
         'HAVE_NETINET_IP_H',
       ],
       'conditions': [
-        ['OS=="aix" or OS=="win"', {
+        ['OS=="aix" or OS=="win" or OS=="os400"', {
           # AIX does not support some of the networking features used in
           # the test server. Windows also lacks the Unix-specific headers
           # and system calls required by the ngtcp2 examples.
@@ -332,7 +332,7 @@
         'HAVE_NETINET_IP_H',
       ],
       'conditions': [
-        ['OS=="aix" or OS=="win"', {
+        ['OS=="aix" or OS=="win" or OS=="os400"', {
           # AIX does not support some of the networking features used in
           # the test client. Windows also lacks the Unix-specific headers
           # and system calls required by the ngtcp2 examples.