[lit] Mark shtest-ulimit.py unsupported on Solaris

There were some build failures because apparently running ulimit -n 50
actually means ulimit -n 48 there. Losing the test coverage on Solaris
shouldn't be a big deal.

Author: boomanaiden154

llvm/utils/lit/tests/shtest-ulimit.py

@@ -1,7 +1,9 @@
 # Check the ulimit command
 
 # ulimit does not work on non-POSIX platforms.
-# UNSUPPORTED: system-windows
+# Solaris for some reason does not respect ulimit -n, so mark it unsupported
+# as well.
+# UNSUPPORTED: system-windows, system-solaris
 
 # RUN: not %{lit} -a -v %{inputs}/shtest-ulimit | FileCheck %s