package/glibc: bump to version 2.29

package/glibc: bump to version 2.29

Changes to build and runtime requirements:

* Python 3.4 or later is required to build the GNU C Library.

* On most architectures, GCC 5 or later is required to build the GNU C
  Library.  (On powerpc64le, GCC 6.2 or later is still required, as
  before.)

While at it, remove the double "glibc-" prefix in the version.

https://www.sourceware.org/ml/libc-alpha/2019-01/msg00723.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>