ada: Fix spelling of functions with(out) "side effects"

ada: Fix spelling of functions with(out) "side effects"

Correct spelling does not include an hyphen. Fix comments and one
error message.

Also fix other mispellings of "side-effect" or "side effect" depending
on the case (adjective should have hyphen), and "side-effect-free" with
double hyphen as an adjective.

gcc/ada/

	* checks.adb, exp_aggr.adb, exp_ch4.ads, exp_ch5.adb,
	exp_util.adb, exp_util.ads, inline.adb, sem_ch13.adb,
	sem_ch6.adb, sem_ch8.adb, sem_prag.adb, sem_util.ads: Fix comments
	and typos.