aarch64: missing side effect of killing flags for clearArray_reg_reg

    In clearArray_reg_reg, we call function: MacroAssembler::zero words(Register ptr, Register cnt).
    This function modifies the flags register by doing a cmp instruction at entry. But this is not reflected in the side effect of clearArray_reg_reg.
    We didn't see this is triggers problems. But this may pose similar risk as bug: 8224828: aarch64: rflags is not correct after safepoint poll.
    Fix is trivial:

diff -r 2342d5af52b7 src/hotspot/cpu/aarch64/aarch64.ad
--- a/src/hotspot/cpu/aarch64/aarch64.ad Mon Jun 22 08:09:23 2020 +0200
+++ b/src/hotspot/cpu/aarch64/aarch64.ad Mon Jun 22 15:58:05 2020 +0800
@@ -13845,7 +13845,7 @@
 instruct clearArray_reg_reg(iRegL_R11 cnt, iRegP_R10 base, Universe dummy, rFlagsReg cr)
 %{
   match(Set dummy (ClearArray cnt base));
- effect(USE_KILL cnt, USE_KILL base);
+ effect(USE_KILL cnt, USE_KILL base, KILL cr);

   ins_cost(4 * INSN_COST);
   format %{ "ClearArray $cnt, $base" %}

BTW: clearArray_imm_reg does not have the issue since it calls a different function: MacroAssembler::zero_words(Register base, u_int64_t cnt)

13843 // clearing of an array
13844
13845 instruct clearArray_reg_reg(iRegL_R11 cnt, iRegP_R10 base, Universe dummy, rFlagsReg cr)
13846 %{
13847 match(Set dummy (ClearArray cnt base));
13848 effect(USE_KILL cnt, USE_KILL base);
13849
13850 ins_cost(4 * INSN_COST);
13851 format %{ "ClearArray $cnt, $base" %}
13852
13853 ins_encode %{
13854 __ zero_words($base$$Register, $cnt$$Register);
13855 %}
13856
13857 ins_pipe(pipe_class_memory);
13858 %}

4771 void MacroAssembler::zero_words(Register ptr, Register cnt)
4772 {
4773 assert(is_power_of_2(zero_words_block_size), "adjust this");
4774 assert(ptr == r10 && cnt == r11, "mismatch in register usage");
4775
4776 BLOCK_COMMENT("zero_words {");
4777 cmp(cnt, (u1)zero_words_block_size); <=================