Enable ccache on Windows CI jobs. (#9801)

  - ccache is now available in OMDev. Enable it when compiling OpenModelica
    with OMDev. This should make checking builds on Windows a bit faster
    once we have the initial ccache.

    The nightly Windows job still builds without ccache. So, in the extreme
    case of something going amiss due to ccache, we will still catch it
    the next day.

Jenkinsfile

@@ -187,7 +187,6 @@ pipeline {
               withEnv (["PATH=C:\\OMDev\\tools\\msys\\usr\\bin;C:\\Program Files\\TortoiseSVN\\bin;c:\\bin\\jdk\\bin;c:\\bin\\nsis\\;${env.PATH};c:\\bin\\git\\bin;"]) {
                 bat "echo PATH: %PATH%"
                 common.buildOMC_CMake('-DCMAKE_BUILD_TYPE=Release'
-                                        + ' -DOM_USE_CCACHE=OFF'
                                         + ' -DCMAKE_INSTALL_PREFIX=build'
                                         + ' -G "MSYS Makefiles"'
                                       )