Use only one process

appveyor.yml

@@ -23,21 +23,21 @@ environment:
         - CC_NAME: Visual Studio 9 2008
           CC_SHORTNAME: vs2008
           # Do not build in parallel, project dependencies are not solved correctly and thus appveyor may randomly fail
-          MAKE: msbuild /m /p:BuildInParallel=false open62541.sln
+          MAKE: msbuild /m:1 /p:BuildInParallel=false open62541.sln
           FORCE_CXX: ON
           OUT_DIR_LIB: bin\Debug
           OUT_DIR_EXAMPLES: bin\examples\Debug
         - CC_NAME: Visual Studio 12 2013
           CC_SHORTNAME: vs2013
           # Do not build in parallel, project dependencies are not solved correctly and thus appveyor may randomly fail
-          MAKE: msbuild /m /p:BuildInParallel=false open62541.sln
+          MAKE: msbuild /m:1 /p:BuildInParallel=false open62541.sln
           FORCE_CXX: OFF
           OUT_DIR_LIB: bin\Debug
           OUT_DIR_EXAMPLES: bin\examples\Debug
         - CC_NAME: Visual Studio 12 2013 Win64
           CC_SHORTNAME: vs2013-x64
           # Do not build in parallel, project dependencies are not solved correctly and thus appveyor may randomly fail
-          MAKE: msbuild /m /p:BuildInParallel=false open62541.sln
+          MAKE: msbuild /m:1 /p:BuildInParallel=false open62541.sln
           FORCE_CXX: OFF
           OUT_DIR_LIB: bin\Debug
           OUT_DIR_EXAMPLES: bin\examples\Debug