Add support to generate locale data

Add support to generate locale data

In order to use locale support on a Linux system, you need locale data
to be present:

 * on a (e)glibc based system, this data is typically in the
   /usr/lib/locale/locale-archive file, which can be created and
   extended using the localedef program

 * on an uClibc based system, the set of supported locales is defined
   at build time by an uClibc configuration option.

This patch implements generating locale data for the following cases:

 * Internal toolchain

 * External toolchain based on (e)glibc. uClibc external toolchains
   are not supported, because with uClibc, the set of supported
   locales is defined at build time. CodeSourcery and Linaro
   toolchains have been tested, Crosstool-NG toolchains are believed
   to work properly as well.

 * Toolchains built using the Crosstool-NG backend, but only (e)glibc
   toolchains.

This feature was runtime tested with internal uClibc toolchain,
CodeSourcery ARM toolchain and Linaro ARM toolchain, thanks to a
simple C program that shows the data and a gettext translated message.

Note that this option differs from the "purge locales" option, which
is responsible for removing translation files and other locale stuff
installed by packages. At some point in the future, we may want to
clarify the respective roles of those options.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>