* Since StackTop=StackBottom+StackLength, any two variables are sufficient to describe stack, the third one is redundant.
* As a first part of cleanup, replaced StackTop with function returning StackBottom+StackLength.
* On Win32 and Win64, StackTop returns the stack base from TIB instead.


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@27119 3ad0048d-3df7-0310-abae-a5850022a9f2