[ADT, Support] Move llvm::numbers to STLForwardCompat.h (NFC) (#164053)

This patch moves llvm::numbers to STLForwardCompat.h for those
constants defined in C++20 to facilitate the migration to C++20.

"float" constants like ef and pif are not part of C++20, so they stay
in MathExtras.h but are reimplemented in terms of e_v, pi_v, etc.

sqrtpi and sqrtpif are not part of C++20, so they also stay in
MathExtras.h, but they are redefined in terms of sqrtpi_v in the same
style as other constants.

I've verified the new C++17-style implementation to be bit-for-bit
identical to the original definitions using static_assert:

  static_assert(e == llvm::numbers_new::e_v<double>);
  static_assert(ef == llvm::numbers_new::e_v<float>);

before replacing the original definitions of e and ef in MathExtras.h,
where llvm::numbers_new was a namesapce I used in STLForwardCompat.h
for testing purposes.

0 files changed, 0 insertions, 0 deletions