Move is_negated_errno() to new header negated_errno.h

Move is_negated_errno() to new header negated_errno.h

Move is_negated_errno() to a separate new header file negated_errno.h
and include it just for architectures which require it.

is_negated_errno() is not used on those architectures
that have a dedicated register to signal a syscall error.

The issue was raised when compiling with clang, which is more
strict regarding semantics of unused static inline functions
defined in C files and will issue a -Wunused-function warrning
if they are not used anywhere.

* syscall.c (is_negated_errno): Move to ...
* negated_errno.h: ... new file.
* Makefile.am (strace_SOURCES): Add it.
* linux/aarch64/get_error.c: Include it.
* linux/arc/get_error.c: Likewise.
* linux/arm/get_error.c: Likewise.
* linux/avr32/get_error.c: Likewise.
* linux/bfin/get_error.c: Likewise.
* linux/crisv10/get_error.c: Likewise.
* linux/hppa/get_error.c: Likewise.
* linux/i386/get_error.c: Likewise.
* linux/ia64/get_error.c: Likewise.
* linux/m68k/get_error.c: Likewise.
* linux/metag/get_error.c: Likewise.
* linux/microblaze/get_error.c: Likewise.
* linux/or1k/get_error.c: Likewise.
* linux/riscv/get_error.c: Likewise.
* linux/s390/get_error.c: Likewise.
* linux/sh/get_error.c: Likewise.
* linux/sh64/get_error.c: Likewise.
* linux/tile/get_error.c: Likewise.
* linux/x86_64/get_error.c: Likewise.
* linux/xtensa/get_error.c: Likewise.