[libcxx] Fix a case of -Wundef warnings. NFC.

Differential Revision: https://reviews.llvm.org/D101978

diff --git a/libcxx/src/locale.cpp b/libcxx/src/locale.cpp
index e352a34..903c78a 100644 (file)
--- a/libcxx/src/locale.cpp
+++ b/libcxx/src/locale.cpp
@@ -1139,7 +1139,7 @@ ctype<char>::classic_table() noexcept
     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();