Rename arch-specific arch_defs.h files to arch_defs_.h

Rename arch-specific arch_defs.h files to arch_defs_.h

Introduce a new arch_defs.h header that includes the corresponding
arch-specific arch_defs_.h file followed by generic arch_defs_.h file.

* linux/arch_defs.h: Rename to linux/arch_defs_.h.
* linux/aarch64/arch_defs.h: Rename to linux/aarch64/arch_defs_.h.
* linux/arm/arch_defs.h: Rename to linux/arm/arch_defs_.h.
* linux/i386/arch_defs.h: Rename to linux/i386/arch_defs_.h.
* linux/m68k/arch_defs.h: Rename to linux/m68k/arch_defs_.h.
* linux/s390/arch_defs.h: Rename to linux/s390/arch_defs_.h.
* linux/s390x/arch_defs.h: Rename to linux/s390x/arch_defs_.h.
* linux/x32/arch_defs.h: Rename to linux/x32/arch_defs_.h.
* linux/x86_64/arch_defs.h: Rename to linux/x86_64/arch_defs_.h.
* arch_defs.h: New file.
* Makefile.am (strace_SOURCES): Add it.
(EXTRA_DIST): Rename linux/*/arch_defs.h to linux/*/arch_defs_.h.