• websocket.c: use Sleep() on Windows.
  sleep() and unistd.h are not available in MSVC.

• http2-upload.c: use local gettimeofday() implementation
  when compiled with MSVC.
  (Alternate solution is to disable the trace function for MSVC.)
  Public domain code copied and adapted from libssh2:
  https://github.com/libssh2/libssh2/blob/e973493f992313b3be73f51d3f7ca6d52e288558/src/misc.c#L719-L743

• silence compiler warning for deprecated inet_addr().
  Also drop duplicate winsock2 include.

  curl\docs\examples\externalsocket.c(125,32): error C2220: the following warning is treated as an error [curl\bld\docs\examples\curl-example-externalsocket.vcxproj]
  curl\docs\examples\externalsocket.c(125,32): warning C4996: 'inet_addr': Use inet_pton() or InetPton() instead or define _WINSOCK_DEPRECATED_NO_WARNINGS to disable deprecated API warnings [curl\bld\docs\examples\curl-example-e
  

  Ref: https://github.com/curl/curl/actions/runs/9227337318/job/25389073450#step:4:95

• silence an MSVC compiler warning. This is in conflict with
  checksrc rules, so silence the rule in favour of the
  warning-free C syntax.

  curl\docs\examples\multi-legacy.c(152,1): error C2220: the following warning is treated as an error [curl\bld\docs\examples\curl-example-multi-legacy.vcxproj]
  curl\docs\examples\multi-legacy.c(152,1): warning C4706: assignment within conditional expression [curl\bld\docs\examples\curl-example-multi-legacy.vcxproj]
  

  Ref: https://github.com/curl/curl/actions/runs/9227337318/job/25389073450#step:4:226

• do not use sys/time.h and unistd.h in Windows builds.
  Some of these includes look unnecessary. Subject to another
  PR.

Cherry-picked from #13766
Closes #13771