ada: Replace redundant conditions with assertions

ada: Replace redundant conditions with assertions

Fix warnings from the CodePeer. The code structure is essentially:

  if A and B then ...
  elsif not A and not B then ...
  elsif A then ...
  elsif B then ...  --  this condition is redundant
  end if;

and it causes CodePeer to say "exception is raised in a conditional
branch", which most likely means that the condition is redundant.

gcc/ada/

	* make.adb (Scan_Make_Arg): Remove redundant condition.
	* switch-b.adb (Scan_Debug_Switches): Likewise.
	* switch-c.adb (Scan_Front_End_Switches): Likewise.