AArch64: fix warnings and errors with Clang and GCC 8.3

These are all AArch64 specific:

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/assembler_aarch64.hpp:279:22: error: & has lower precedence than ==; == will be evaluated first [-Werror,-Wparentheses]
    assert_cond(bits & mask == mask);
                     ^~~~~~~~~~~~~~
                                                                                                                                                                                               /home/nicgas01/jdk/src/hotspot/cpu/aarch64/interp_masm_aarch64.hpp:44:25: error: redeclaration of using declaration
  using MacroAssembler::call_VM_leaf_base;
        ~~~~~~~~~~~~~~~~^


/home/nicgas01/jdk/src/hotspot/cpu/aarch64/aarch64.ad:13866:80: error: invalid suffix 'D' on floating constant
    __ fcmps(as_FloatRegister(opnd_array(1)->reg(ra_,this,idx1)/* src1 */), 0.0D);
                                                                               ^

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/c1_LIRGenerator_aarch64.cpp:429:66: error: implicit conversion of NULL constant to 'bool' [-Werror,-Wnull-conversion]
  arithmetic_op_fpu(x->op(), reg, left.result(), right.result(), NULL);
  ~~~~~~~~~~~~~~~~~ ^~~~
                                                                 false

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp:1074:24: error: '&&' within '||' [-Werror,-Wlogical-op-parentheses]
      if (is_unordered && op->cond() == lir_cond_equal
          ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/copy_linux_aarch64.s:162:32: error: index must be a multiple of 8 in range [0, 32760].
        prfm pldl1keep, [s, #-256]
                               ^

/home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp:43:39: error: cannot initialize a parameter of type 'char *' with an lvalue of type 'unsigned long'
    return __sync_add_and_fetch(dest, add_value);
                                      ^~~~~~~~~

/home/nicgas01/jdk/src/hotspot/share/runtime/atomic.hpp:659:45: note: in instantiation of function template specialization 'Atomic::PlatformAdd<8>::add_and_fetch<unsigned long, char *>' requ\
ested here
  return static_cast<const Derived*>(this)->add_and_fetch(add_value, dest, order);
                                            ^

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp:2684:17: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
    offset &= -1<<12;
              ~~^
                                                                                                                                                                                               /home/nicgas01/jdk/src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp:679:8: error: conflicting types for '_Copy_conjoint_jshorts_atomic'
  void _Copy_conjoint_jshorts_atomic(jshort* from, jshort* to, size_t count) {
       ^

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp:177:13: error: using the result of an assignment as a condition without parentheses [-Werror,-Wparentheses]
      if (p = strchr(buf, ':')) {
          ~~^~~~~~~~~~~~~~~~~~

/home/nicgas01/jdk/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp:2684:17: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
    offset &= -1<<12;
              ~~^