[Makefile.in] glibc: Remove unnecessary -g option

Using llvm-objdump I found warning if file was
compiled using riscv-gcc. Examples:

warning: failed to find source riscv-glibc/csu/elf-init.c

It concerned with compilation glibc with
debug info that is unnecessary operation. If user want to have debug info, than it's easy to pass -g.

This option wasn't touched more than 7 years...