Revert "[clang] Mark clang-format-ignore.cpp as unsupported on Windows"

This reverts commit dc61ebb.

See llvm#76733 (comment).

(cherry picked from commit a628f68)

Author: owenca

clang/test/Format/clang-format-ignore.cpp

@@ -1,4 +1,3 @@
-// UNSUPPORTED: system-windows
 // RUN: rm -rf %t.dir
 // RUN: mkdir -p %t.dir/level1/level2