Merge ~info-martin-konrad/epics-base:explicitly-specify-appveyor-worker-image into ~epics-core/epics-base/+git/epics-base:3.15

[Martin Konrad]

AppVeyor kept using "Visual Studio 2019" if not specified explicitly although the documentation says it should default to "Visual Studio 2015". Specifying the worker image explicitly fixes these problems.

[Andrew Johnson (anj)]

No objections; I haven't tested this myself though.

[Martin Konrad (info-martin-konrad)]

With this change the build succeeds: https://ci.appveyor.com/project/MartinKonrad/epics-base/builds/32153795

[Andrew Johnson (anj)]

Merging.

review: Approve

diff --git a/appveyor.yml b/appveyor.yml
index ff829f8..bc04839 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -40,14 +40,18 @@ configuration:
 # Environment variables: compiler toolchain
 environment:
   matrix:
-  - TOOLCHAIN: 10.0
-  - TOOLCHAIN: 11.0
-  - TOOLCHAIN: 12.0
-  - TOOLCHAIN: 14.0
+  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    TOOLCHAIN: 10.0
+  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    TOOLCHAIN: 11.0
+  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    TOOLCHAIN: 12.0
+  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    TOOLCHAIN: 14.0
   - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
     TOOLCHAIN: 2017
-  - TOOLCHAIN: mingw
-    APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+    TOOLCHAIN: mingw
 
 # Platform: architecture
 platform: