[configure] Use hg, instead of svn, to compute the version string

Now we moved from Subversion to Mercurial, use the hg command to
compute the version string.

Manually backported from 1409:7264ce426be4 plus 1430:933eee133cbf
as too much changes have been made to ./configure in the meantime.

# x86_64 specific options

config ARCH_x86_64

    select ARCH_64

    select ARCH_SUPPORT_ARCH

    select ARCH_SUPPORT_CPU

    select ARCH_SUPPORT_TUNE

    help

      The x86_64 architecture, as defined by:

        http://www.amd.com/us-en/Processors/DevelopWithAMD/0,,30_2252_875_7044,00.html