[lldb][test] Disable TestChildCountTruncation on Windows

This fails because it tells clang to use DWARF which link.exe
then discards.

The test may not need DWARF, but I'm going to confirm that in
a follow up PR review.

Test added by #149088.

Author: DavidSpickett

lldb/test/Shell/Settings/TestChildCountTruncation.test

@@ -1,6 +1,9 @@
 # Test that we warn the user about truncated output
 # when target.max-children-count wasn't explicitly set.
 
+# link.exe discards the DWARF information needed.
+# UNSUPPORTED: system-windows
+
 # RUN: split-file %s %t
 # RUN: %clang_host -g -gdwarf %t/main.cpp -o %t.out
 # RUN: %lldb -x -b -s %t/dwim-commands.input %t.out -o exit 2>&1 \