LibJS: Define Date constants such that translation units don't copy them

Variables that are constexpr must be delcared inline in the global
namespace to prevent copying them.

The static keyword is meaningless on variables in headers in the global
namespace. Declare the static bigint as extern and define it out-of-line
instead.

Userland/Libraries/LibJS/Runtime/Date.cpp

@@ -21,6 +21,8 @@ static Crypto::SignedBigInteger const s_one_billion_bigint { 1'000'000'000 };
 static Crypto::SignedBigInteger const s_one_million_bigint { 1'000'000 };
 static Crypto::SignedBigInteger const s_one_thousand_bigint { 1'000 };
 
+Crypto::SignedBigInteger const ns_per_day_bigint { static_cast<i64>(ns_per_day) };
+
 NonnullGCPtr<Date> Date::create(Realm& realm, double date_value)
 {
     return realm.heap().allocate<Date>(realm, date_value, *realm.intrinsics().date_prototype());

Userland/Libraries/LibJS/Runtime/Date.h

@@ -31,22 +31,22 @@ private:
 };
 
 // https://tc39.es/ecma262/#eqn-HoursPerDay
-constexpr double hours_per_day = 24;
+constexpr inline double hours_per_day = 24;
 // https://tc39.es/ecma262/#eqn-MinutesPerHour
-constexpr double minutes_per_hour = 60;
+constexpr inline double minutes_per_hour = 60;
 // https://tc39.es/ecma262/#eqn-SecondsPerMinute
-constexpr double seconds_per_minute = 60;
+constexpr inline double seconds_per_minute = 60;
 // https://tc39.es/ecma262/#eqn-msPerSecond
-constexpr double ms_per_second = 1'000;
+constexpr inline double ms_per_second = 1'000;
 // https://tc39.es/ecma262/#eqn-msPerMinute
-constexpr double ms_per_minute = 60'000;
+constexpr inline double ms_per_minute = 60'000;
 // https://tc39.es/ecma262/#eqn-msPerHour
-constexpr double ms_per_hour = 3'600'000;
+constexpr inline double ms_per_hour = 3'600'000;
 // https://tc39.es/ecma262/#eqn-msPerDay
-constexpr double ms_per_day = 86'400'000;
+constexpr inline double ms_per_day = 86'400'000;
 // https://tc39.es/proposal-temporal/#eqn-nsPerDay
-constexpr double ns_per_day = 86'400'000'000'000;
-static auto const ns_per_day_bigint = "86400000000000"_sbigint;
+constexpr inline double ns_per_day = 86'400'000'000'000;
+extern Crypto::SignedBigInteger const ns_per_day_bigint;
 
 u16 day_within_year(double);
 u8 date_from_time(double);