Misc cleanups found while working on transient scopes.
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* comperr.adb (Compiler_Abort): Call Sinput.Unlock, because if
this is called late, then Source_Dump would crash otherwise.
* debug.adb: Correct documentation
Use Tbuild.Unchecked_Convert_To instead of
Nmake.Make_Unchecked_Type_Conversion. This leads to more readable source
code in the compiler, and also more readable .dg code, because it
removes redundant unchecked conversions.
There is only one remaining call to Make_Unchecked_Type_Conversion,
which i
