libc/{glibc,eglibc}: Don't download glibc-ports when not available

Don't download glibc-ports when glibc or eglibc version greater than 2.16,
because the "ports" source is mainline in the glibc or eglibc since version 2.17.

Signed-off-by: "Daniel Zimmermann" <netzimme@gmail.com>
Message-Id: <9c045ca3cf1b9dc89da3.1384602843@haus-VirtualBox>
Patchwork-Id: 291766
[yann.morin.1998@free.fr: slightly tweak subject, change variable name]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 # MIPS specific config options

 ## select ARCH_SUPPORTS_32

 ## select ARCH_SUPPORTS_64 if EXPERIMENTAL

 ## select ARCH_DEFAULT_32

 ## select ARCH_USE_MMU

 ## select ARCH_SUPPORTS_BOTH_ENDIAN

 ## select ARCH_DEFAULT_BE

 ## select ARCH_SUPPORTS_WITH_ARCH

 ## select ARCH_SUPPORTS_WITH_TUNE

 ## select ARCH_SUPPORTS_WITH_FLOAT

 ##

 ## help The MIPS architecture, as defined by:

 ## help     http://www.mips.com/