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>

# Blackfin specific configuration file

## select ARCH_SUPPORTS_32

## select ARCH_DEFAULT_32

## select ARCH_DEFAULT_LE

## select ARCH_SUPPORT_ARCH

## select ARCH_SUPPORT_CPU

## select ARCH_SUPPORT_TUNE

## select ARCH_SUPPORT_FPU

##

## help The Blackfin architecture