Fix Spec/Body headers in .adb/.ads files, respectively; all violations
detected with grep and manually filtered because of .tmpl files.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* exp_atag.adb, lib-util.ads, libgnat/g-decstr.adb,
	libgnat/g-exptty.adb, libgnat/g-socpol.adb,
	libgnat/s-strhas.adb: Fix headers.