Add Mac x86_64 and Win x86_64 to target platform in parent pom

Plugin configuration for org.eclipse.tycho:target-platform-configuration does not intentionally specify the Mac x86_64 and Win x86_64 environments since these entries break XulRunner build.

However, QE would like to run SWTBot tests also on these environments and overriding the configuration in every bot test plugin is probably not a good idea.

One solution could be to specify those environments in parent pom and override it only in XullRunner's pom file (the requirement not to specify the environments would be clearly defined and documented for XullRunner).

Other solution might be to specify a profile that we could activate on the command line that would add those two environments to the plugin's configuration.