Similar to <concepts>, we need to protect the header and test against inclusion and being run if concepts aren't supported by the compiler. Differential Revision: https://reviews.llvm.org/D82171
Summary: Constants have 33 significant decimal digits for IEEE 754 128-bit floating-point numbers. Reviewers: ldionne, #libc, EricWF, zoecarver, curdeius Reviewed By: ldionne, #libc, curdeius Differential Revision: https://reviews.llvm.org/D77505