don't use Bash-specific ${parameter/pattern/string} expansion

don't use Bash-specific ${parameter/pattern/string} expansion

sysdeps/unix/make-syscalls.sh and sysdeps/unix/Makefile use GNU Bash's
${parameter/pattern/string} parameter expansion.  Non-Bash shells (e.g.
dash or BusyBox ash when built with CONFIG_ASH_BASH_COMPAT disabled)
don't support this expansion syntax.  So glibc will fail to build when
$(SHELL) expands to a path that isn't provided by Bash.

An example build failure:

    for dir in [...]; do \
      test -f $dir/syscalls.list && \
      { sysdirs='[...]' \
        asm_CPP='gcc -c    -I[...]   -D_LIBC_REENTRANT -include include/libc-symbols.h       -DASSEMBLER  -g -Wa,--noexecstack   -E -x assembler-with-cpp' \
        /bin/sh sysdeps/unix/make-syscalls.sh $dir || exit 1; }; \
      test $dir = sysdeps/unix && break; \
    done > [build-dir]/sysd-syscallsT
    sysdeps/unix/make-syscalls.sh: line 273: syntax error: bad substitution

This patch simply replaces the three instances of the Bash-only syntax
in these files with an echo and sed command substitution.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>