[libc++] Fix unrepresentable enum for clang-cl unstable ABI

[bcraig]

Summary

When using LIBCXX_ABI_UNSTABLE=YES, clang-cl gave the following warning:

P:\llvm_master\src\llvm\projects\libcxx\include\string(683,51):
warning: enumerator value is not representable in the underlying type
'int' [-Wmicrosoft-enum-value]

Fixed by switching from enums to static const size_type.

[EricWF]

Maybe using a static const variable instead of an enum would work better? __long_mask should never actually be ODR used so a definition for it should never actually be needed.

[bcraig]

Switched to static consts

[EricWF]

LGTM.

include/__config

 #ifdef _LIBCPP_HAS_NO_STRONG_ENUMS
 #define _LIBCPP_DECLARE_STRONG_ENUM(x) struct _LIBCPP_TYPE_VIS x { enum __lx
 #define _LIBCPP_DECLARE_STRONG_ENUM_EPILOG(x) \
     __lx __v_; \
     _LIBCPP_ALWAYS_INLINE x(__lx __v) : __v_(__v) {} \
     _LIBCPP_ALWAYS_INLINE explicit x(int __v) : __v_(static_cast<__lx>(__v)) {} \
     _LIBCPP_ALWAYS_INLINE operator int() const {return __v_;} \
     };
+#define _LIBCPP_UNDERLYING_ENUM_TYPE(t)
 #else  // _LIBCPP_HAS_NO_STRONG_ENUMS
 #define _LIBCPP_DECLARE_STRONG_ENUM(x) enum class _LIBCPP_ENUM_VIS x
 #define _LIBCPP_DECLARE_STRONG_ENUM_EPILOG(x)
+#define _LIBCPP_UNDERLYING_ENUM_TYPE(t) : t
 #endif  // _LIBCPP_HAS_NO_STRONG_ENUMS
 
 #ifdef _LIBCPP_DEBUG
 #   if _LIBCPP_DEBUG == 0
 #       define _LIBCPP_DEBUG_LEVEL 1
 #   elif _LIBCPP_DEBUG == 1
 #       define _LIBCPP_DEBUG_LEVEL 2
 #   else

include/string

struct __long
         size_type __cap_;
     };
 
 #if _LIBCPP_BIG_ENDIAN
     enum {__short_mask = 0x01};
     enum {__long_mask  = 0x1ul};
 #else  // _LIBCPP_BIG_ENDIAN
     enum {__short_mask = 0x80};
-    enum {__long_mask  = ~(size_type(~0) >> 1)};
+    enum _LIBCPP_UNDERLYING_ENUM_TYPE(size_type) {__long_mask  = ~(size_type(~0) >> 1)};
 #endif  // _LIBCPP_BIG_ENDIAN
 
     enum {__min_cap = (sizeof(__long) - 1)/sizeof(value_type) > 2 ?
                       (sizeof(__long) - 1)/sizeof(value_type) : 2};
 
     struct __short
     {
         value_type __data_[__min_cap];
#else
     {
         size_type __cap_;
         size_type __size_;
         pointer   __data_;
     };
 
 #if _LIBCPP_BIG_ENDIAN
     enum {__short_mask = 0x80};
-    enum {__long_mask  = ~(size_type(~0) >> 1)};
+    enum _LIBCPP_UNDERLYING_ENUM_TYPE(size_type) {__long_mask  = ~(size_type(~0) >> 1)};
 #else  // _LIBCPP_BIG_ENDIAN
     enum {__short_mask = 0x01};
     enum {__long_mask  = 0x1ul};
 #endif  // _LIBCPP_BIG_ENDIAN
 
     enum {__min_cap = (sizeof(__long) - 1)/sizeof(value_type) > 2 ?
                       (sizeof(__long) - 1)/sizeof(value_type) : 2};