[Ada] armhf-linux: symbolic tracebacks

gcc/ada/

	* libgnat/s-objrea.ads (Object_Arch): Add ARM enum
	* libgnat/s-objrea.adb (Initialize): Add EM_ARM case.
	(Read_Address): Add ARM case to 32bit read.
	* Makefile.rtl: Add trasym units to the runtime for armhf-linux.