Make building perl on Win32 with the free VC++ toolkit easier

Make building perl on Win32 with the free VC++ toolkit easier

Introduce new CCTYPE's MSVC70FREE and MSVC70 for the free and the full
versions of MS VC++ 7.x respectively.  Perl can now be built with the
free VC++ toolkit simply by running "nmake CCTYPE=MSVC70FREE" with no
hacking of the win32/Makefile required.  Update README.win32 with
these changes.

Also add the CCTYPE MSVC to win32/Makefile.  This is already supported
in win32/makefile.mk and is useful for avoiding the use of -DELAYLOAD
for MS VC++ 3.x through 5.x.  Update README.win32 for this too.

p4raw-id: //depot/perl@25672