Large-scale warning fixes in Windows-only code

[Stephan Bergmann]

I finally managed to get our Clang loplugin working with clang-cl on 
Windows.  This caused lots of warnings, in Windows-only code (as the 
generic code is routinely run against the loplugin on Linux and macOS 
already), that have been fixed in a bunch of recent master commits, 
split into one commit per code module.

Many of the fixes are trivial, semi-automated ones, but some are not. 
And the likelihood of regressions is certainly non-zero in such an 
amount of changes.  However, the nature of such all-across-the-codebase 
changes makes it hard to adequately test for regressions upfront.

Hence this heads up:  If you come across any Windows-only regressions on 
master, it might be to do with this bunch of changes.  They got split 
into the following three blocks:

* 974b7fe6dfa8935a2068365e416b8d886f9d2a32 "clang-cl loplugin: sal" from 
Oct 4

* 
613213240a84327a0a72bb5ee98cc88d50c1fd0e--85876a11ceb9bf144ae8365ff3a9fedd8c363ef2 
"clang-cl loplugin: xmlsecurity--shell" from Oct 15

* 
918d85a82d6535932118247a7fb754dde9f49cd1--6d4f7734ad63998b067f50b6564639a527bf34e3 
"clang-cl loplugin: sfx2--avmedia" from Oct 16