* lib/fenv.in.h (feclearexcept, feraiseexcept, fetestexcept): New
declarations.
* lib/fenv-except-tracking-clear.c: New file, based on glibc.
* lib/fenv-except-tracking-raise.c: New file, based on glibc.
* lib/fenv-except-tracking-test.c: New file, based on glibc.
* m4/fenv-exceptions-tracking.m4: New file.
* m4/fenv-exceptions.m4: New file.
* modules/fenv-exceptions-tracking-c99: New file.
* doc/posix-functions/feclearexcept.texi: Mention the new module.
* doc/posix-functions/fetestexcept.texi: Likewise.
* doc/posix-functions/feraiseexcept.texi: Likewise. Mention the glibc
and Cygwin bugs.