do we still care about building with gcc-4.9?

[Alan Modra]

gcc-4.9 does not like the parentheses or cast in AARCH64_FIELD when
used in an initialiser:

opcodes/aarch64-opc-2.c:29:3: error: initializer element is not constant
   {AARCH64_OPND_CLASS_INT_REG, "Rd", OPD_F_HAS_INSERTER | OPD_F_HAS_EXTRACTOR, {AARCH64_FIELD (0, 5)}, "an integer register"},
   ^
opcodes/aarch64-opc-2.c:29:3: error: (near initialization for ‘aarch64_operands[1].fields[0]’)

-- 
Alan Modra