Add functions declared in ctype.h to builtin function database. All functions are annotated with nothrow and const attribute, which enables better optimization.
Fix attribute annotation from 'const' to 'pure'. Add support for 'pure' attribute to builtin function database related code. Test case (test/Sema/libbuiltins-ctype.c) added. Line 116 of test/FixIt/typo.m is removed because it is not necessary for test but causes a warning that cannot be addressed by -fixit once isupper is registered to Builtins.def.