Update the way we handle directories supplied by the user:
- the tarball directory is considered as a local copy, and tarballs are copied to a working area,
- the sources and build directories (CT_SRC_DIR and CT_BUILD_DIR) are now computed, and no longer an option,
- the build dir has been renamed from 'build' to 'targets'.
That should ease preparing a tarball of the resulting target.

 --- gcc-4.0.0/libstdc++-v3/include/c_std/std_cstdio.h-orig	2005-04-29 00:08:41.000000000 -0500

 +++ gcc-4.0.0/libstdc++-v3/include/c_std/std_cstdio.h	2005-04-29 00:08:45.000000000 -0500

 @@ -142,7 +142,7 @@

    using ::vsprintf;

  }

 -#if _GLIBCXX_USE_C99

 +#if _GLIBCXX_USE_C99 || defined(__UCLIBC__)

  #undef snprintf

  #undef vfscanf