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