Bug 19075 – rt.util.random.Rand48.defaultSeed should prefer RDTSC or mach_absolute_time or QueryPerformanceCounter to ctime.time

`rt.util.random.Rand48.defaultSeed` generates a seed from the clock using `ctime.time`. With `D_InlineAsm_X86_64` it would be better to use the `rdtsc` instruction because it is much faster as well as being finer precision. (Finer precision is a benefit not because we care about accurate time, but because the differences between seeds generated this way are potentially greater.) The same is true of `mach_absolute_time` on macOS. The Microsoft Windows equivalent would be `QueryPerformanceCounter` but I haven't benchmarked it to verify that it is faster than `ctime.time`.

Verified that QueryPerformanceCounter is faster.

Commits pushed to master at https://github.com/dlang/druntime https://github.com/dlang/druntime/commit/449ef5265e46d57000bfb5a745b2be5856325e1e Fix Issue 19075 - rt.util.random.Rand48.defaultSeed should prefer RDTSC or mach_absolute_time or QueryPerformanceCounter to ctime.time `rt.util.random.Rand48.defaultSeed` generates a seed from the clock using `ctime.time`. With `D_InlineAsm_X86_64` it would be better to use the RDTSC instruction because it is much faster as well as being finer precision. (Finer precision is a benefit not because we care about accurate time, but because the differences between seeds generated this way are potentially greater.) The same is true of `mach_absolute_time` on macOS and `QueryPerformanceCounter` on Microsoft Windows. This PR doesn't use RDTSC with `D_InlineAsm_X86` because some x86 processors don't support RDTSC and because on x86 (but not x86-64) Linux `prctl` can disable a process's ability to use RDTSC. https://github.com/dlang/druntime/commit/b3edb173828b75c23d3e2bd8614389d4a5ccb845 Merge pull request #2248 from n8sh/rt-defaultSeed-rdtsc Fix Issue 19075 - rt.util.random.Rand48.defaultSeed should prefer RDTSC or mach_absolute_time or QueryPerformanceCounter to ctime.time