Add BAZEL_VC and JAVA_HOME to build_windows_jni.sh
Add BAZEL_VC and JAVA_HOME to build_windows_jni.sh

User might have Visual C++ Build Tools and JDK installed at non-default location, but they are still usable for bootstrapping.

PS: I used Visual C++ 2017 15.3 for bootstrapping, there is a nice 1.5MB size reduction in final `bazel.exe` compared with `bazel-0.7.0-without-jdk-windows-x86_64.exe`.

Closes #3943.

PiperOrigin-RevId: 177815687

perezd/bazel,werkt/bazel,katre/bazel,ulfjack/bazel,ButterflyNetwork/bazel,cushon/bazel,bazelbuild/bazel,davidzchen/bazel,safarmer/bazel,akira-baruah/bazel,safarmer/bazel,akira-baruah/bazel,akira-baruah/bazel,cushon/bazel,werkt/bazel,safarmer/bazel,aehlig/bazel,aehlig/bazel,bazelbuild/bazel,aehlig/bazel,bazelbuild/bazel,bazelbuild/bazel,dslomov/bazel-windows,dropbox/bazel,davidzchen/bazel,dropbox/bazel,aehlig/bazel,ButterflyNetwork/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,meteorcloudy/bazel,davidzchen/bazel,aehlig/bazel,katre/bazel,safarmer/bazel,werkt/bazel,twitter-forks/bazel,katre/bazel,ulfjack/bazel,twitter-forks/bazel,dslomov/bazel,ButterflyNetwork/bazel,akira-baruah/bazel,meteorcloudy/bazel,dslomov/bazel,twitter-forks/bazel,werkt/bazel,safarmer/bazel,perezd/bazel,meteorcloudy/bazel,dslomov/bazel,dslomov/bazel-windows,meteorcloudy/bazel,cushon/bazel,perezd/bazel,ulfjack/bazel,perezd/bazel,davidzchen/bazel,ulfjack/bazel,cushon/bazel,cushon/bazel,akira-baruah/bazel,safarmer/bazel,twitter-forks/bazel,aehlig/bazel,davidzchen/bazel,dropbox/bazel,twitter-forks/bazel,ulfjack/bazel,dropbox/bazel,dslomov/bazel,perezd/bazel,ButterflyNetwork/bazel,perezd/bazel,davidzchen/bazel,katre/bazel,dslomov/bazel,perezd/bazel,ButterflyNetwork/bazel,ulfjack/bazel,dslomov/bazel,bazelbuild/bazel,twitter-forks/bazel,meteorcloudy/bazel,dslomov/bazel-windows,werkt/bazel,akira-baruah/bazel,dslomov/bazel,katre/bazel,bazelbuild/bazel,davidzchen/bazel,cushon/bazel,werkt/bazel,dslomov/bazel-windows,meteorcloudy/bazel,ulfjack/bazel,twitter-forks/bazel,dslomov/bazel-windows,dropbox/bazel,katre/bazel,dslomov/bazel-windows,dropbox/bazel,aehlig/bazel