test: add cygwin feature and use it (test 1056, 1517)

To replace custom checks with the same effect.

Closes #18327

tests/data/test1056

@@ -45,10 +45,10 @@ body
 # This test relies on the IPv6 scope field being ignored when connecting to
 # ipv6-localhost (i.e. [::1%259999] is treated as [::1]). Maybe this is a bit
 # dodgy, but it happens on all our test platforms but Windows so skip this
-# test there. This feature doesn't work on msys or Cygwin, so use a precheck
-# to skip those.
+# test there. Not supported on the Windows kernel, this includes MSYS2/Cygwin.
 <features>
 IPv6
+!cygwin
 !win32
 </features>
 <server>
@@ -61,9 +61,6 @@ HTTP follow redirect from IPv4 to IPv6 with scope
 <command>
 http://%HOSTIP:%HTTPPORT/we/are/all/twits/%TESTNUMBER -L
 </command>
-<precheck>
-%PERL -e "print 'Test is not supported on the Windows kernel' if($^O eq 'MSWin32' || $^O eq 'msys' || $^O eq 'cygwin');"
-</precheck>
 </client>
 
 #

tests/data/test1517

@@ -36,6 +36,11 @@ This is a virtual description of server virtual error.
 
 # Client-side
 <client>
+# Windows TCP does not deliver response data but reports CONNABORTED
+<features>
+!cygwin
+!win32
+</features>
 <server>
 http
 </server>
@@ -43,12 +48,6 @@ http
 <tool>
 lib%TESTNUMBER
 </tool>
-# precheck is a command line to run before the test, to see if we can execute
-# the test or not
-<precheck>
-%LIBTESTS lib%TESTNUMBER check
-</precheck>
-
 <name>
 HTTP POST, server responds before completed send
 </name>