[AArch64] Only check breakpoint alignment on inserting

[AArch64] Only check breakpoint alignment on inserting

This patch fixes the GDB internal error on AArch64 when running
watchpoint-fork.exp

 top?bt 15
 internal_error (file=file@entry=0x79d558 "../../binutils-gdb/gdb/linux-nat.c", line=line@entry=4866, fmt=0x793b20 "%s: Assertion `%s' failed.")
    at ../../binutils-gdb/gdb/common/errors.c:51
 #1  0x0000000000495bc4 in linux_nat_thread_address_space (t=<optimized out>, ptid=<error reading variable: Cannot access memory at address 0x1302>)
    at ../../binutils-gdb/gdb/linux-nat.c:4866
 #2  0x00000000005db2c8 in delegate_thread_address_space (self=<optimized out>, arg1=<error reading variable: Cannot access memory at address 0x1302>)
    at ../../binutils-gdb/gdb/target-delegates.c:2447
 #3  0x00000000005e8c7c in target_thread_address_space (ptid=<error reading variable: Cannot access memory at address 0x1302>)
    at ../../binutils-gdb/gdb/target.c:2727
 #4  0x000000000054eef8 in get_thread_arch_regcache (ptid=..., gdbarch=0xad51e0) at ../../binutils-gdb/gdb/regcache.c:529
 #5  0x000000000054efcc in get_thread_regcache (ptid=...) at ../../binutils-gdb/gdb/regcache.c:546
 #6  0x000000000054f120 in get_thread_regcache_for_ptid (ptid=...) at ../../binutils-gdb/gdb/regcache.c:560
 #7  0x00000000004a2278 in aarch64_point_is_aligned (is_watchpoint=0, addr=34168, len=2) at ../../binutils-gdb/gdb/nat/aarch64-linux-hw-point.c:122
 #8  0x00000000004a2e68 in aarch64_handle_breakpoint (type=hw_execute, addr=34168, len=2, is_insert=0, state=0xae8880)
    at ../../binutils-gdb/gdb/nat/aarch64-linux-hw-point.c:465
 #9  0x000000000048edf0 in aarch64_linux_remove_hw_breakpoint (self=<optimized out>, gdbarch=<optimized out>, bp_tgt=<optimized out>)
    at ../../binutils-gdb/gdb/aarch64-linux-nat.c:657
 #10 0x00000000005da8dc in delegate_remove_hw_breakpoint (self=<optimized out>, arg1=<optimized out>, arg2=<optimized out>)
    at ../../binutils-gdb/gdb/target-delegates.c:492
 #11 0x0000000000536a24 in bkpt_remove_location (bl=<optimized out>) at ../../binutils-gdb/gdb/breakpoint.c:13065
 #12 0x000000000053351c in remove_breakpoint_1 (bl=0xb3fe70, is=is@entry=mark_inserted) at ../../binutils-gdb/gdb/breakpoint.c:4026
 #13 0x000000000053ccc0 in detach_breakpoints (ptid=...) at ../../binutils-gdb/gdb/breakpoint.c:3930
 #14 0x00000000005a3ac0 in handle_inferior_event_1 (ecs=0x7ffffff048) at ../../binutils-gdb/gdb/infrun.c:5042

After the fork, GDB will physically remove the breakpoints from the child
process (in frame #14), but at that time, GDB doesn't create an inferior
yet for child, but inferior_ptid is set to child's ptid (in frame #13).
In aarch64_point_is_aligned, we'll get the regcache of current_lwp_ptid
to determine if the current process is 32-bit or 64-bit, so the inferior
can't be found, and the internal error is caused.

I don't find a better fix other than not checking alignment on removing
breakpoint.

gdb:

2015-11-27  Yao Qi  <yao.qi@linaro.org>

	* nat/aarch64-linux-hw-point.c (aarch64_dr_state_remove_one_point):
	Don't assert on alignment.
	(aarch64_handle_breakpoint): Only check alignment when IS_INSERT
	is true.