Rename module fenv to fenv-h. * modules/fenv-h: Renamed from modules/fenv. * modules/fenv-h-tests: Renamed from modules/fenv-tests. * modules/fenv-h-c++-tests: Renamed from modules/fenv-c++-tests. * tests/test-fenv-h.c: Renamed from tests/test-fenv.c. * tests/test-fenv-h-c++.cc: Renamed from tests/test-fenv-c++.cc. * doc/posix-headers/fenv.texi: Update. * modules/* (Depends-on): Update. * modules/fenv: New file.