On evc4 the ptrdiff_t is missing. In branch 5.0 for
both evc3 and evc4 the ptrdiff_t was defined. In
current CVS HEAD it seems it isn't. This patch corrects
The patch additionally adds a check if _STLP_DEBUG is
defined when compiling with the ARM compiler for
evc3/evc4. This mode is known to not work due to a
compiler bug (hopefully fixed in msvc8-ARM).