Fix compilation of WinCE. Change the fixed UNICODE define of WinCE to FPC_OS_UNICODE, so that it won't be undefined when changing the mode/string type and that the usage of a UNICODE API is independant of the mode.

Also adjusted all Windows (Win32/64/CE) units to define a "UNICODE" if "FPC_OS_UNICODE" is defined (except the Jedi units).
Also the common RTL units that checked for UNICODE now check for FPC_OS_UNICODE.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@24420 3ad0048d-3df7-0310-abae-a5850022a9f2