libc/glibc: fix {e,}glibc add-ons with short or long names

Fixes the issue with {e,}glibc addons having short and long names (such as
eglibc-ports-2_13 and ports), which caused configure scripts to run
through them twice and thus configuring incorrectly.

For instance, the mips64el-n32-linux-gnu toolchain would be recognized
correctly first, but then the second pass would change it to mips32,
building a mixed MIPS-III N32 and MIPS-I libc.

Signed-off-by: Nicolás Reynolds <fauno@kiwwwi.com.ar>
[yann.morin.1992@anciens.enib.fr: remove spurious trailing spaces]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from af25723a794f2017f45c300369a6d36849e22236)

 # Dummy config file to not use a C library *at all*

 # depends on BARE_METAL

 config LIBC_none

     help

       Do not use a C library.

       This is usefull if your project is self-contained, does not rely on

       an external C library, and provides all the necessary bits.

       Most probably usefull to bootloaders, as they generally don't depend

       on the C library.

       If unsure: do *not* choose that, and use another option in the choice.