[Ada] Fix varsize node name conflict

gcc/ada/

	* gen_il-gen.adb, gen_il-internals.ads: Generate field
	enumeration literals with "F_" prefix.  Update all generated
	references accordingly.
	* atree.adb, einfo-utils.adb, sem_ch3.adb, sem_ch5.adb,
	sem_ch6.adb, sem_ch8.adb, sinfo-cn.adb, sinfo-utils.adb,
	sinfo-utils.ads, treepr.adb: Add "F_" prefix to all uses of the
	field enumeration literals.
12 files changed