libc/eglibc: fix downloading of localedef addon

For the versions of eglibc where the ports addon is not external (ie,
all versions after, and including 2.17), we would fail to download the
localedef addon, since the test did not care about the addon we were
about to download, only whether the ports addon was external or not.

Fix that by skipping the ports addon only if that's the addon we're
trying to download.

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

 # windows config options

 ## depends on ARCH_x86

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 ## select WINDOWS

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 ## help Build a toolchain targeting systems running Windows as host