* lib/fenv.in.h (fegetexceptflag, fesetexceptflag): New declarations.
* lib/fenv-except-state-get.c: New file, baed on glibc.
* lib/fenv-except-state-set.c: New file, baed on glibc.
* m4/mathfunc.m4 (gl_MATHFUNC): Handle also the 'fexcept_t *' type.
* m4/fenv-exceptions-state.m4: New file.
* modules/fenv-exceptions-state-c99: New file.
* doc/posix-functions/fegetexceptflag.texi: Mention the new module.
* doc/posix-functions/fesetexceptflag.texi: Mention the new module and
the glibc, musl libc, macOS, AIX, mingw bugs.