[Ada] Fix bogus style check failure with pragma Style_Checks (Off)

[Pierre-Marie de Rodat]

This fixes a bogus style check failure for long lines in rare cases
where the compiler is invoked, with a -gnatyX switch where X is neither
'm' nor 'M', on a unit which contains "with" clauses for other units
that contain a pragma Style_Checks (Off).

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

2019-08-13  Eric Botcazou  <ebotca...@adacore.com>

gcc/ada/

        * sem.adb (Do_Analyze): Recompute Style_Check_Max_Line_Length
        after restoring Style_Max_Line_Length.
--- gcc/ada/sem.adb
+++ gcc/ada/sem.adb
@@ -1395,6 +1395,7 @@ package body Sem is
          Restore_Scope_Stack  (List);
          Restore_Ghost_Region (Saved_GM, Saved_IGR);
          Style_Max_Line_Length := Saved_ML;
+         Style_Check_Max_Line_Length := Style_Max_Line_Length /= 0;
       end Do_Analyze;
 
       --  Local variables