* lib/fenv.in.h (feenableexcept, fedisableexcept, fegetexcept): New
declarations.
* lib/fenv-except-trapping.c: New file, based on glibc.
* m4/fenv_h.m4 (gl_FENV_H): Test also whether fegetexcept is declared.
* m4/fenv-exceptions-trapping.m4: New file.
* modules/fenv-exceptions-trapping: New file.
* doc/glibc-functions/fegetexcept.texi: Mention the new module.
* doc/glibc-functions/fedisableexcept.texi: Likewise.
* doc/glibc-functions/feenableexcept.texi: Likewise. Mention the glibc,
macOS, FreeBSD bugs.