* lib/fenv.in.h (fenv_t) [hppa]: Remove the __exception field.
(FE_DFL_ENV): Override if <fenv.h> exists but HAVE_FE_DFL_ENV is not
defined.
(fegetenv, fesetenv, feupdateenv, feholdexcept): New declarations.
* lib/fenv-env.c: New file, based on glibc.
* lib/fenv-env-hold.c: New file.
* lib/fenv-env-update.c: New file.
* m4/fenv-environment.m4: New file.
* m4/mathfunc.m4 (gl_MATHFUNC): Handle also the 'fenv_t *' type.
* m4/fenv_h.m4 (gl_FENV_H_DEFAULTS): Initialize REPLACE_FEGETENV,
REPLACE_FEHOLDEXCEPT, REPLACE_FESETENV, REPLACE_FEUPDATEENV.
* modules/fenv (Makefile.am): Substitute REPLACE_FEGETENV,
REPLACE_FEHOLDEXCEPT, REPLACE_FESETENV, REPLACE_FEUPDATEENV.
* modules/fenv-environment: New file.
* doc/posix-functions/fegetenv.texi: Mention the new module and the bugs
on glibc, macOS, AIX.
* doc/posix-functions/feholdexcept.texi: Mention the new module and the
bugs on glibc, musl libc, FreeBSD, AIX, mingw, MSVC.
* doc/posix-functions/fesetenv.texi: Mention the new module and the bugs
on musl libc, FreeBSD, NetBSD, AIX, Solaris, Cygwin, mingw, MSVC.
* doc/posix-functions/feupdateenv.texi: Mention the new module and the
bugs on glibc, musl libc, macOS, FreeBSD, AIX, Solaris, mingw, MSVC.