Comment on why we pin to Visual Studio 2015.

Change-Id: Iaa0dd108c3a446b64f0a0effdcae97d521226792
Reviewed-on: https://code-review.googlesource.com/c/re2/+/44224
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/kokoro/bazel.sh b/kokoro/bazel.sh
index 2a21167..75edc02 100755
--- a/kokoro/bazel.sh
+++ b/kokoro/bazel.sh
@@ -6,7 +6,7 @@
 case "${KOKORO_JOB_NAME}" in
   */windows-*)
     choco upgrade bazel -y -i
-    # The automagical configuration seems to break. :/
+    # Pin to Visual Studio 2015, which is the minimum that we support.
     export BAZEL_VC='C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC'
     ;;
   *)
diff --git a/kokoro/cmake.sh b/kokoro/cmake.sh
index 999fbfe..bee1943 100755
--- a/kokoro/cmake.sh
+++ b/kokoro/cmake.sh
@@ -5,6 +5,7 @@
 
 case "${KOKORO_JOB_NAME}" in
   */windows-*)
+    # Pin to Visual Studio 2015, which is the minimum that we support.
     CMAKE_G_A_FLAGS=('-G' 'Visual Studio 14 2015' '-A' 'x64')
     ;;
   *)