(is_arm_mapping_symbol_name): New function - return true when a symbol name

(is_arm_mapping_symbol_name): New function - return true when a symbol name
 matches the requirements for an ARM mapping symbol name.
(arm_elf_find_function): New function based on elf_find_function in elf.c but
 skipping ARM mapping symbols and including thumb function symbols.
(elf32_arm_find_nearest_line): Use arm_elf_find_function.
(elf32_arm_output_symbol_hook): Use is_arm_mapping_symbol_name.