On MacOS X, we used to use the native perl interpreter from /usr/bin.
Unfortunately, that interpreter fails to build a number of packages
(Subversion, Git, etc. ...), because it assumes knowledge about the
underlying C compiler that is not valid for the compiler used by Nix.
For example, /usr/bin/perl assumes that the compiler can build binaries
for both the ppc and the x86 architecture. /usr/bin/gcc can do that, but
the gcc from Nix can't.
The solution is to compile Perl 5.10 in Nix so that the ./configure
phase can properly detect the system's capabilities. However, note that
the resulting binary is impure: it will find headers in /usr/include and
libraries in /usr/lib. In this respect, the Nix-compiled perl binary is
no different than the native one in /usr/bin -- it's just configured
more accurately.
svn path=/nixpkgs/trunk/; revision=17870
