address a few compiler warnings

src/u_ceproject.pas

@@ -838,7 +838,7 @@ end;
 procedure TNativeProject.checkSemantics;
 var
   i: integer;
-  s: string;
+  s: string = '';
   d: DCompiler;
 begin
   i := currentConfiguration.otherOptions.customOptions.Count;

src/u_gdb.pas

@@ -1928,7 +1928,7 @@ var
   gdb: string;
   i: integer;
   b: TPersistentBreakPoint;
-  o: TDebugeeOption;
+  o: TDebugeeOption = nil;
 const
   asmFlavorStr: array[TAsmSyntax] of string = ('intel','att');
 begin

src/u_infos.pas

@@ -118,7 +118,7 @@ end;
 procedure TToolInfo.refreshStatus;
 var
   pth: string;
-  cmp: DCompiler;
+  cmp: DCompiler = DCompiler.dmd;
 begin
   if fLabel.isNotAssigned or fStatus.isNotAssigned then
     exit;

src/u_miniexplorer.pas

@@ -372,8 +372,10 @@ begin
 end;
 
 destructor TMiniExplorerWidget.destroy;
+{$if lcl_fullversion >= 2020000}
 var
   i: integer;
+{$endif}
 begin
 
   fMnxSubj.free;

src/u_synmemo.pas

@@ -3998,6 +3998,7 @@ end;
 
 function gutterIconKindToColumn(value: TGutterIcon): integer;
 begin
+  result := 0;
   case value of
     giBreakSet     : result := 1;
     giBulletGreen  : result := 2;