Use default cpp fmt build script.

vendor/Fmt/support/appveyor.yml

@@ -0,0 +1,31 @@
+configuration:
+  - Debug
+  - Release
+
+clone_depth: 1
+
+image:
+  - Visual Studio 2015
+
+platform:
+  - x64
+
+environment:
+  CTEST_OUTPUT_ON_FAILURE: 1
+  MSVC_DEFAULT_OPTIONS: ON
+  BUILD: msvc
+
+before_build:
+ - mkdir build
+ - cd build
+
+build_script:
+  - python ../support/appveyor-build.py
+
+on_failure:
+  - appveyor PushArtifact Testing/Temporary/LastTest.log
+  - appveyor AddTest test
+
+# Uncomment this to debug AppVeyor failures.
+#on_finish:
+#  - ps: $blockRdp = $true; iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-rdp.ps1'))