Add support for aarch64, powerpc64 and riscv64.
Add native support for arm.

Index: gdb/Makefile.in
--- gdb/Makefile.in.orig
+++ gdb/Makefile.in
@@ -728,6 +728,7 @@ ALL_64_TARGET_OBS = \
 	aarch64-fbsd-tdep.o \
 	aarch64-linux-tdep.o \
 	aarch64-newlib-tdep.o \
+	aarch64-obsd-tdep.o \
 	aarch64-ravenscar-thread.o \
 	aarch64-tdep.o \
 	alpha-bsd-tdep.o \
@@ -766,9 +767,11 @@ ALL_64_TARGET_OBS = \
 	mips-sde-tdep.o \
 	mips-tdep.o \
 	mips64-obsd-tdep.o \
+	ppc64-obsd-tdep.o \
 	riscv-fbsd-tdep.o \
 	riscv-linux-tdep.o \
 	riscv-none-tdep.o \
+	riscv-obsd-tdep.o \
 	riscv-ravenscar-thread.o \
 	riscv-tdep.o \
 	sparc64-fbsd-tdep.o \
@@ -1477,6 +1480,7 @@ HFILES_NO_SRCDIR = \
 	riscv-fbsd-tdep.h \
 	riscv-ravenscar-thread.h \
 	riscv-tdep.h \
+	riscv-obsd-tdep.h \
 	rs6000-aix-tdep.h \
 	run-on-main-thread.h \
 	s390-linux-tdep.h \
@@ -1681,6 +1685,8 @@ ALLDEPFILES = \
 	aarch64-linux-nat.c \
 	aarch64-linux-tdep.c \
 	aarch64-newlib-tdep.c \
+	aarch64-obsd-nat.c \
+	aarch64-obsd-tdep.c \
 	aarch64-ravenscar-thread.c \
 	aarch64-tdep.c \
 	aix-thread.c \
@@ -1719,6 +1725,7 @@ ALLDEPFILES = \
 	arm-netbsd-nat.c \
 	arm-netbsd-tdep.c \
 	arm-none-tdep.c \
+	arm-obsd-nat.c \
 	arm-obsd-tdep.c \
 	arm-tdep.c \
 	avr-tdep.c \
@@ -1820,6 +1827,8 @@ ALLDEPFILES = \
 	ppc-ravenscar-thread.c \
 	ppc-sysv-tdep.c \
 	ppc64-tdep.c \
+	ppc64-obsd-nat.c \
+	ppc64-obsd-tdep.c \
 	procfs.c \
 	ravenscar-thread.c \
 	remote-sim.c \
@@ -1830,6 +1839,8 @@ ALLDEPFILES = \
 	riscv-none-tdep.c \
 	riscv-ravenscar-thread.c \
 	riscv-tdep.c \
+	riscv-obsd-nat.c \
+	riscv-obsd-tdep.c \
 	rl78-tdep.c \
 	rs6000-aix-nat.c \
 	rs6000-lynx178-tdep.c \
