Attempt to fix MSVC build broken by r294326

MSVC does not think that `char []` can be constexpr. Switch to regular const.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294327 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/Chrono.h

@@ -76,21 +76,15 @@ raw_ostream &operator<<(raw_ostream &OS, sys::TimePoint<> TP);
 ///  display unit or you request that the unit is not displayed.
 
 namespace detail {
-template <typename Period> struct unit { static constexpr char value[] = ""; };
-template <typename Period> constexpr char unit<Period>::value[];
-
-template <> struct unit<std::ratio<3600>> {
-  static constexpr char value[] = "h";
-};
-
-template <> struct unit<std::ratio<60>> {
-  static constexpr char value[] = "m";
-};
-
-template <> struct unit<std::ratio<1>> { static constexpr char value[] = "s"; };
-template <> struct unit<std::milli> { static constexpr char value[] = "ms"; };
-template <> struct unit<std::micro> { static constexpr char value[] = "us"; };
-template <> struct unit<std::nano> { static constexpr char value[] = "ns"; };
+template <typename Period> struct unit { static const char value[]; };
+template <typename Period> const char unit<Period>::value[] = "";
+
+template <> struct unit<std::ratio<3600>> { static const char value[]; };
+template <> struct unit<std::ratio<60>> { static const char value[]; };
+template <> struct unit<std::ratio<1>> { static const char value[]; };
+template <> struct unit<std::milli> { static const char value[]; };
+template <> struct unit<std::micro> { static const char value[]; };
+template <> struct unit<std::nano> { static const char value[]; };
 } // namespace detail
 
 template <typename Rep, typename Period>

lib/Support/Chrono.cpp

@@ -16,12 +16,12 @@ namespace llvm {
 
 using namespace sys;
 
-constexpr char detail::unit<std::ratio<3600>>::value[];
-constexpr char detail::unit<std::ratio<60>>::value[];
-constexpr char detail::unit<std::ratio<1>>::value[];
-constexpr char detail::unit<std::milli>::value[];
-constexpr char detail::unit<std::micro>::value[];
-constexpr char detail::unit<std::nano>::value[];
+const char detail::unit<std::ratio<3600>>::value[] = "h";
+const char detail::unit<std::ratio<60>>::value[] = "m";
+const char detail::unit<std::ratio<1>>::value[] = "s";
+const char detail::unit<std::milli>::value[] = "ms";
+const char detail::unit<std::micro>::value[] = "us";
+const char detail::unit<std::nano>::value[] = "ns";
 
 static inline struct tm getStructTM(TimePoint<> TP) {
   struct tm Storage;