Fix (most) OpenBSD link errors

Fix (most) OpenBSD link errors

This fixes these errors:
ld: error: undefined symbol: x86_stopped_by_hw_breakpoint()
>>> referenced by x86-nat.h:109 (../../gdb/x86-nat.h:109)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::stopped_by_hw_breakpoint())

ld: error: undefined symbol: x86_can_use_hw_breakpoint(bptype, int, int)
>>> referenced by x86-nat.h:76 (../../gdb/x86-nat.h:76)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::can_use_hw_breakpoint(bptype, int, int))

ld: error: undefined symbol: x86_insert_hw_breakpoint(gdbarch*, bp_target_info*)
>>> referenced by x86-nat.h:93 (../../gdb/x86-nat.h:93)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::insert_hw_breakpoint(gdbarch*, bp_target_info*))

ld: error: undefined symbol: x86_remove_hw_breakpoint(gdbarch*, bp_target_info*)
>>> referenced by x86-nat.h:97 (../../gdb/x86-nat.h:97)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::remove_hw_breakpoint(gdbarch*, bp_target_info*))

ld: error: undefined symbol: x86_remove_watchpoint(unsigned long, int, target_hw_bp_type, expression*)
>>> referenced by x86-nat.h:89 (../../gdb/x86-nat.h:89)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::remove_watchpoint(unsigned long, int, target_hw_bp_type, expression*))

ld: error: undefined symbol: x86_insert_watchpoint(unsigned long, int, target_hw_bp_type, expression*)
>>> referenced by x86-nat.h:84 (../../gdb/x86-nat.h:84)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::insert_watchpoint(unsigned long, int, target_hw_bp_type, expression*))

ld: error: undefined symbol: x86_stopped_by_watchpoint()
>>> referenced by x86-nat.h:100 (../../gdb/x86-nat.h:100)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::stopped_by_watchpoint())

ld: error: undefined symbol: x86_stopped_data_address(unsigned long*)
>>> referenced by x86-nat.h:103 (../../gdb/x86-nat.h:103)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::stopped_data_address(unsigned long*))

ld: error: undefined symbol: x86_region_ok_for_hw_watchpoint(unsigned long, int)
>>> referenced by x86-nat.h:79 (../../gdb/x86-nat.h:79)
>>>               amd64-obsd-nat.o:(x86_nat_target<obsd_nat_target>::region_ok_for_hw_watchpoint(unsigned long, int))

and

ld: error: undefined symbol: x86_dr_insert_watchpoint(x86_debug_reg_state*, target_hw_bp_type, unsigned long, int)
>>> referenced by x86-nat.c:156 (../../gdb/x86-nat.c:156)
>>>               x86-nat.o:(x86_insert_watchpoint(unsigned long, int, target_hw_bp_type, expression*))

ld: error: undefined symbol: x86_dr_remove_watchpoint(x86_debug_reg_state*, target_hw_bp_type, unsigned long, int)
>>> referenced by x86-nat.c:169 (../../gdb/x86-nat.c:169)
>>>               x86-nat.o:(x86_remove_watchpoint(unsigned long, int, target_hw_bp_type, expression*))

ld: error: undefined symbol: x86_dr_region_ok_for_watchpoint(x86_debug_reg_state*, unsigned long, int)
>>> referenced by x86-nat.c:181 (../../gdb/x86-nat.c:181)
>>>               x86-nat.o:(x86_region_ok_for_hw_watchpoint(unsigned long, int))

ld: error: undefined symbol: x86_dr_stopped_data_address(x86_debug_reg_state*, unsigned long*)
>>> referenced by x86-nat.c:194 (../../gdb/x86-nat.c:194)
>>>               x86-nat.o:(x86_stopped_data_address(unsigned long*))

ld: error: undefined symbol: x86_dr_stopped_by_watchpoint(x86_debug_reg_state*)
>>> referenced by x86-nat.c:206 (../../gdb/x86-nat.c:206)
>>>               x86-nat.o:(x86_stopped_by_watchpoint())

ld: error: undefined symbol: x86_dr_insert_watchpoint(x86_debug_reg_state*, target_hw_bp_type, unsigned long, int)
>>> referenced by x86-nat.c:219 (../../gdb/x86-nat.c:219)
>>>               x86-nat.o:(x86_insert_hw_breakpoint(gdbarch*, bp_target_info*))

ld: error: undefined symbol: x86_dr_remove_watchpoint(x86_debug_reg_state*, target_hw_bp_type, unsigned long, int)
>>> referenced by x86-nat.c:233 (../../gdb/x86-nat.c:233)
>>>               x86-nat.o:(x86_remove_hw_breakpoint(gdbarch*, bp_target_info*))

ld: error: undefined symbol: x86_dr_stopped_by_hw_breakpoint(x86_debug_reg_state*)
>>> referenced by x86-nat.c:269 (../../gdb/x86-nat.c:269)
>>>               x86-nat.o:(x86_stopped_by_hw_breakpoint())

It does not fix:
ld: error: can't create dynamic relocation R_X86_64_64 against symbol: __gmp_binvert_limb_table in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
>>> defined in /usr/local/lib/libgmp.a(mp_minv_tab.o)
>>> referenced by tmp-dive_1.s
>>>               dive_1.o:(__gmpn_divexact_1) in archive /usr/local/lib/libgmp.a

ld: error: can't create dynamic relocation R_X86_64_64 against symbol: __gmp_binvert_limb_table in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
>>> defined in /usr/local/lib/libgmp.a(mp_minv_tab.o)
>>> referenced by tmp-bdiv_q_1.s
>>>               bdiv_q_1.o:(__gmpn_bdiv_q_1) in archive /usr/local/lib/libgmp.a

ld: error: can't create dynamic relocation R_X86_64_64 against symbol: __gmpn_invert_limb_table in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
>>> defined in /usr/local/lib/libgmp.a(invert_limb_table.o)
>>> referenced by tmp-invert_limb.s
>>>               invert_limb.o:(__gmpn_invert_limb) in archive /usr/local/lib/libgmp.a

gdb/ChangeLog:

2019-12-04  Christian Biesinger  <cbiesinger@google.com>

	* configure.nat (obsd64): Add missing files x86-nat.o and
	nat/x86-dregs.o.

Change-Id: I4a443c0cf805efd7b45feaabd729a01b07772724