Fix baseTools hardcode ECP_SOURCE as %WORKSPACE%/EdkCompatibilityPkg, now if ECP_SOURCE has exist in OS environment, will use the value form OS environment.
Fix baseTools hardcode ECP_SOURCE as %WORKSPACE%/EdkCompatibilityPkg, now if ECP_SOURCE has exist in OS environment, will use the value form OS environment.

git-svn-id: f3880c1fc5096ce2109c8aec392d8e07f619f417@2125 c2973edb-eda0-4c78-bc6a-9341b269661f

bitcrystal/buildtools-BaseTools,tianocore/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,tianocore/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,tianocore/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,tianocore/buildtools-BaseTools,tianocore/buildtools-BaseTools