Backwards compatibility patch for cross-compilation changes.

Changes back the types of 'configCompiler' and 'configCompilerEx', but marks
them as deprecated. Adds new functions 'configCompilerEx' and
'configCompilerAuxEx'.

The remaining functions that changed type after the cross-compilation changes
shouldn't matter from the backwards compatibility standpoint:

    * InstallDirs.{absoluteInstallDirs, prefixRelativeInstallDirs,
      initialPathTemplateEnv} - the versions in D.S.LocalBuildInfo retain their
      old types and are usually used instead. In any case, removing the Platform
      parameter from here is problematic because the default install dirs now
      include $arch and $os vars.

    * D.S.Configure.configure - shouldn't be used by the setup scripts.

See #1214 for the original (backwards-incompatible) patches.
Merge pull request #1429 from 23Skidoo/issue1214-backwards-compat

Backwards compatibility patch for cross-compilation changes.