Fix several 'reaches end of function' warnings by making fatal noreturn.

The warnings also pointed out a few genuine bugs. Replace some tabs with
spaces.

dmd/mars.h

@@ -412,7 +412,12 @@ void warning(Loc loc, const char *format, ...) IS_PRINTF(2);
 void vwarning(Loc loc, const char *format, va_list);
 void error(Loc loc, const char *format, ...) IS_PRINTF(2);
 void verror(Loc loc, const char *format, va_list);
+
+#ifdef __GNUC__
+__attribute__((noreturn))
+#endif
 void fatal();
+
 void err_nomem();
 void inifile(char *argv0, const char *inifile);
 void halt();

gen/complex.cpp

@@ -456,7 +456,9 @@ DValue* DtoCastComplex(Loc& loc, DValue* val, Type* _to)
         DImValue* re = new DImValue(extractty, repart);
         return DtoCastFloat(loc, re, to);
     }
-    else
+    else {
         error(loc, "Don't know how to cast %s to %s", vty->toChars(), to->toChars());
+        fatal();
+    }
 }
 

gen/irstate.cpp

@@ -39,6 +39,7 @@ const IRScope& IRScope::operator=(const IRScope& rhs)
     begin = rhs.begin;
     end = rhs.end;
     builder.SetInsertPoint(begin);
+    return *this;
 }
 
 //////////////////////////////////////////////////////////////////////////////////////////

gen/linker.cpp

@@ -204,8 +204,10 @@ int linkExecutable(const char* argv0)
         error("linking failed:\nstatus: %d", status);
         if (!errstr.empty())
             error("message: %s", errstr.c_str());
-        fatal();
+        return status;
     }
+
+    return 0;
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -339,14 +341,16 @@ int linkObjToExecutable(const char* argv0)
     // terminate args list
     args.push_back(NULL);
 
-    // try to call linker!!!
+    // try to call linker
     if (int status = llvm::sys::Program::ExecuteAndWait(gcc, &args[0], NULL, NULL, 0,0, &errstr))
     {
         error("linking failed:\nstatus: %d", status);
         if (!errstr.empty())
             error("message: %s", errstr.c_str());
-        fatal();
+        return status;
     }
+    
+    return 0;
 }
 
 //////////////////////////////////////////////////////////////////////////////

gen/main.cpp

@@ -960,8 +960,7 @@ LDC_TARGETS
     else
     {
         if (global.params.link)
-            //status = runLINK();
-            linkObjToExecutable(global.params.argv0);
+            status = linkObjToExecutable(global.params.argv0);
 
         if (global.params.run)
         {