In GCC5 the preprocessor changed the format of its line number output,
breaking the alien_svn build. Until this is fixed upstream, work around
the issue by disabling preprocessor line numbering.
The absence of alien_svn made the git_svn subpackage uninstallable on
x86_64.
See "Preprocessor issues" in: https://gcc.gnu.org/gcc-5/porting_to.html
* Referring the current haiku version explicitly is not needed, since
the RequiresUpdater takes care of setting the version of Haiku used
for building a package.
