[arm] fix bootstrap failure due to uninitialized warning

The Arm port is failing bootstrap because GCC is now warning about an
unitialized array.

The code is complex enough that I certainly can't be sure the compiler
is wrong, so perhaps the best fix here is just to memset the entire
array before use.

	* config/arm/arm.c (neon_valid_immediate): Clear bytes before use.

From-SVN: r277073

gcc/ChangeLog

+2019-10-16  Richard Earnshaw  <rearnsha@arm.com>
+
+	* config/arm/arm.c (neon_valid_immediate): Clear bytes before use.
+
 2019-10-16  Mihailo Stojanovic  <mistojanovic@wavecomp.com>
 
 	* config/mips/mips.c (mips_expand_builtin_insn): Force the

gcc/config/arm/arm.c

@@ -12233,7 +12233,7 @@ neon_valid_immediate (rtx op, machine_mode mode, int inverse,
 
   unsigned int i, elsize = 0, idx = 0, n_elts;
   unsigned int innersize;
-  unsigned char bytes[16];
+  unsigned char bytes[16] = {};
   int immtype = -1, matches;
   unsigned int invmask = inverse ? 0xff : 0;
   bool vector = GET_CODE (op) == CONST_VECTOR;