[libc++][format] Fix a missing include in tests.

diff --git a/libcxx/test/support/format.functions.common.h b/libcxx/test/support/format.functions.common.h
index 769b1aff9c6425e91f0b5aae02f8eefa7a66110b..81ed04998a5103d9b81d7f23e49bf788650b61fb 100644 (file)
--- a/libcxx/test/support/format.functions.common.h
+++ b/libcxx/test/support/format.functions.common.h
@@ -11,6 +11,7 @@
 // Contains the common part of the formatter tests for different papers.
 
 #include <algorithm>
+#include <cctype>
 #include <charconv>
 #include <format>
 #include <ranges>