Use arch variable for platform switch

Author: alexey.gadzhiev

.appveyor.yml

@@ -12,16 +12,14 @@ platform:
 - x64
 - x86
 environment:
-  matrix:
-  - arch: Win64
-  # - arch: #does not work, Release|x64 not a valid target
+  arch: Win64
 matrix:
   fast_finish: true
 
 # skip unsupported combinations
 init:
-- set arch=
-- if "%arch%"=="Win64" ( set arch= Win64)
+- if "%PLATFORM%"=="x86" ( set arch=)
+- if "%PLATFORM%"=="x64" ( set arch= Win64)
 - echo %arch%
 - echo %PLATFORM%
 - echo %APPVEYOR_BUILD_WORKER_IMAGE%