libc/eglibc: use generic SVN functions

eglibc is only available from SVN. The script currently calls svn
in its own tortuous and convoluted way.

Use the egeneric SVN extract functions, and sinplify the eglibc
download function.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Alpha specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_USE_MMU

 ## select ARCH_SUPPORT_CPU

 ## select ARCH_SUPPORT_TUNE

 ##

 ## help The Alpha architecture.