MdeModulePkg: Fix constructor invocation ordering

The BaseSerialPortLib16550 library does not implement
a constructor. This prevents the correct constructor
invocation order for dependent libraries.
e.g. A PlatformHookLib (for the Serial Port) may have
a dependency on retrieving data from a Hob. A Hob
library implementation may configure its initial state
in the HobLib constructor. Since BaseSerialPortLib16550
does not implement a constructor, the Basetools do not
resolve the correct order for constructor invocation.

To fix this, add an empty constructor to the serial port
library BaseSerialPortLib16550.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Ard Biesheuvel <Ard.Biesheuvel@arm.com>
Acked-by: Hao A Wu <hao.a.wu@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>

MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.inf

@@ -2,6 +2,8 @@
 #  SerialPortLib instance for 16550 UART.
 #
 #  Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2020, ARM Limited. All rights reserved.
+#
 #  SPDX-License-Identifier: BSD-2-Clause-Patent
 #
 ##
@@ -14,6 +16,7 @@
   MODULE_TYPE                    = BASE
   VERSION_STRING                 = 1.1
   LIBRARY_CLASS                  = SerialPortLib
+  CONSTRUCTOR                    = BaseSerialPortLib16550
 
 [Packages]
   MdePkg/MdePkg.dec