libc/glibc: normalize glibc hidden version names

Hidden version names for glibc conflicted:

LIBC_GLIBC_V_2.10.1
LIBC_V_2.10

name them constantly as:
LIBC_GLIBC_V_<version>

Reported-by: Esben Haabendal <eha@doredevelopment.dk>
Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>

reporter_name="Yann E. MORIN"

reporter_url="http://ymorin.is-a-geek.org/projects/crosstool"

reporter_comment="Experimental toolchain for ARM cortex-m3 in Thumb-only, noMMU, and newlib."