glibc: add 2.24

since eglibc is deprecated just use glibc as name

- fix build errors w. stack-protector (observed for x86_64):
libresolv_pic.a(gethnamaddr.os): In function `addrsort':
gethnamaddr.c:(.text+0x425): undefined reference to `__stack_chk_guard'

by additionally setting libc_cv_ssp_strong=no
like previously libc_cv_ssp=no was set

- fix compile errors on 2.24 x86 introduced by
upstream changesets "Optimize i386 syscall inlining"

errors are like:
- https://sourceware.org/ml/libc-alpha/2015-10/msg00745.html
and trying to fix with the whats suggested at:
https://patchwork.openembedded.org/patch/118909/
leads to other error:
gcc6: elf/librtld.os: In function `__mmap':
(.text+0x131a9): undefined reference to `__libc_do_syscall'
or:
gcc5: elf/dl-load.os
{standard input}: Assembler messages:
{standard input}:5129: Error: symbol `__x86.get_pc_thunk.cx' is already defined

instead of testing other flags/effects (-fno-omit-frame-pointer)
just use -O2 (like buildroot does) instead of -Os

boot+pings tested on:
qemu malta (le+be) (gcc5+bin2.25.1)
qemu aarch64 (gcc5+bin2.25.1)
qemu x86_64 (gcc6+bin2.26)
qemu x86 generic (gcc6+bin2.26)

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>