Windows: BAZEL_VC and BAZEL_VS may be quoted
Windows: BAZEL_VC and BAZEL_VS may be quoted

windows_cc_configure.bzl now accepts BAZEL_VC and
BAZEL_VS even if they are quoted.

windows_cc_configure.bzl now also displays a
warning [1] if BAZEL_VC or BAZEL_VS points to a
non-existent directory.

[1] when warnings are enabled through
CC_CONFIGURE_DEBUG=1

Fixes https://github.com/bazelbuild/bazel/issues/8310

RELNOTES: Windows, C++ autoconfigure: BAZEL_VC and BAZEL_VS may now have quotes, so if you set these envvars' values in cmd.exe via TAB-completion then you no longer need to remove the surrounding quotes.

Closes #8314.

PiperOrigin-RevId: 248126273

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