[ARM] Access FPSCR on vfpv2

GDB can fetch or store FPSCR on vfpv3, which has 32 VFP registers, but
fail to do so on vfpv2, which has 16 VFP registers.  GDB code is incorrect
for vfpv2,

       else if (tdep->vfp_register_count > 0
 	       && regno >= ARM_D0_REGNUM
	       && regno <= ARM_D0_REGNUM + tdep->vfp_register_count)

while FPSCR register number is defined as ARM_D0_REGNUM + 32.

  ARM_D0_REGNUM,		/* VFP double-precision registers.  */
  ARM_D31_REGNUM = ARM_D0_REGNUM + 31,
  ARM_FPSCR_REGNUM,

The code above uses "<=" rather than "<", in order to put FPSCR in the
range, but it is only correct when tdep->vfp_register_count is 32.  On
vpfv2, it is 16, and FPSCR is out of the range, so fetch_vfp_regs or
store_vfp_regs are not called.

gdb:

2017-07-25  Yao Qi  <[email protected]>

	PR tdep/21717
	* arm-linux-nat.c (arm_linux_fetch_inferior_registers): Update
	condition for FPSCR.
	(arm_linux_store_inferior_registers): Likewise.

gdb/ChangeLog

@@ -1,3 +1,10 @@
+2017-07-25  Yao Qi  <[email protected]>
+
+	PR tdep/21717
+	* arm-linux-nat.c (arm_linux_fetch_inferior_registers): Update
+	condition for FPSCR.
+	(arm_linux_store_inferior_registers): Likewise.
+
 2017-07-22  Tom Tromey  <[email protected]>
 
 	* break-catch-syscall.c (struct catch_syscall_inferior_data)

gdb/arm-linux-nat.c

@@ -402,7 +402,8 @@ arm_linux_fetch_inferior_registers (struct target_ops *ops,
 	fetch_wmmx_regs (regcache);
       else if (tdep->vfp_register_count > 0
 	       && regno >= ARM_D0_REGNUM
-	       && regno <= ARM_D0_REGNUM + tdep->vfp_register_count)
+	       && (regno < ARM_D0_REGNUM + tdep->vfp_register_count
+		   || regno == ARM_FPSCR_REGNUM))
 	fetch_vfp_regs (regcache);
     }
 }
@@ -439,7 +440,8 @@ arm_linux_store_inferior_registers (struct target_ops *ops,
 	store_wmmx_regs (regcache);
       else if (tdep->vfp_register_count > 0
 	       && regno >= ARM_D0_REGNUM
-	       && regno <= ARM_D0_REGNUM + tdep->vfp_register_count)
+	       && (regno < ARM_D0_REGNUM + tdep->vfp_register_count
+		   || regno == ARM_FPSCR_REGNUM))
 	store_vfp_regs (regcache);
     }
 }