[libcxx] Fix a case of -Wundef warnings. NFC.
Differential Revision: https://reviews.llvm.org/D101978
GitOrigin-RevId: dafbfb1d1d8e01beac3704aea4e8df45260a6310
diff --git a/src/locale.cpp b/src/locale.cpp
index e352a34..903c78a 100644
--- a/src/locale.cpp
+++ b/src/locale.cpp
@@ -1139,7 +1139,7 @@
return _C_ctype_tab_ + 1;
#elif defined(__GLIBC__)
return _LIBCPP_GET_C_LOCALE->__ctype_b;
-#elif __sun__
+#elif defined(__sun__)
return __ctype_mask;
#elif defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
return __pctype_func();