[PATCH 5.6.2] MSWin32 test & compilation warning fixes

How about applying the following patches to the 5.6.2 branch?

  #10684

This is the important one, as it makes ext/IPC/SysV/t/*.t
skip all tests if IPC::SysV wasn't built.

The following patches are optional, as they only fix MSVC++
compilation warnings:

  #10526
  #10537
  #11744

My attached patch removes 4 other warnings (these were part
of the bigger changes #10335 and #13267).

With all five patches applied, there's only 1 warning left
during compilation (not sure how/if this [cs]hould be fixed):

  C:\Programme\MSVS\VC98\include\stddef.h(78) : warning C4005: 'errno' : macro redefinition
        ..\..\lib\CORE\win32iop.h(186) : see previous definition of 'errno'

And I get:

  All tests successful, 31 tests and 197 subtests skipped.

-- Marcus

• [PATCH 5.6.2] MSWin32 test & compilation warning fixes by Marcus Holland-Moritz
• Re: [PATCH 5.6.2] MSWin32 test & compilation warning fixes by Rafael Garcia-Suarez