libc: Move xtensa reentrant syscall impl to common libc-hooks

The xcc specific reentrant syscall implementations are actually useful
for xtensa in general.  So move that code from being specific to
intel_s1000 / xcc into generic newlib/libc-hooks.c.  This is in prep
for the Zephyr SDK dropping -DMISSING_SYSCALL_NAMES which will make
its version of newlib on xtensa match behavior with xcc.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
2 files changed