RFR: Fix Windows build failures

[Aleksey Shipilev]

Current Windows builds fail with:

c:\buildbot\worker\build-shenandoah-jdkx-windows\build\src\hotspot\share\gc\shenandoah\shenandoahScanRemembered.cpp(36): error C2220: the following warning is treated as an error
c:\buildbot\worker\build-shenandoah-jdkx-windows\build\src\hotspot\share\gc\shenandoah\shenandoahScanRemembered.cpp(36): warning C4267: '=': conversion from 'size_t' to 'uint32_t', possible loss of data
make[3]: *** [lib/CompileJvm.gmk:143: /cygdrive/c/buildbot/worker/build-shenandoah-jdkx-windows/build/build/windows-x86_64-server-fastdebug/hotspot/variant-server/libjvm/objs/shenandoahScanRemembered.obj] Error 1

Additional testing:
 - [x] Windows builds

-------------

Commit messages:
 - Fix Windows build failures

Changes: https://git.openjdk.java.net/shenandoah/pull/17/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=17&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/17.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/17/head:pull/17

PR: https://git.openjdk.java.net/shenandoah/pull/17