OvmfPkg XenPkg: X64 DEBUG GCC5 -DDEBUG_ON_SERIAL_PORT=TRUE build is broken

["Rebecca Cran" <rebecca@bsdio.com>]

I was trying to build OvmfPkg/XenPkg -a X64 -t GCC5 -b DEBUG 
-DDEBUG_ON_SERIAL_PORT=TRUE, but the build fails. Both plain DEBUG and 
RELEASE builds without trying to put the debug output on the serial port 
work.


[bcran@smic ~/src/tmp/edk2]$ build -p OvmfPkg/OvmfXen.dsc -a X64 -t GCC5 
-b DEBUG -DDEBUG_ON_SERIAL_PORT=TRUE
Build environment: FreeBSD-13.0-CURRENT-amd64-64bit-ELF
Build start time: 11:59:24, Apr.14 2020

WORKSPACE        = /home/bcran/src/tmp/edk2
EDK_TOOLS_PATH   = /home/bcran/src/tmp/edk2/BaseTools
CONF_PATH        = /home/bcran/src/tmp/edk2/Conf
PYTHON_COMMAND   = /usr/local/bin/python3


Processing meta-data .
Architecture(s)  = X64
Build target     = DEBUG
Toolchain        = GCC5

Active Platform          = /home/bcran/src/tmp/edk2/OvmfPkg/OvmfXen.dsc
.

build.py...
/home/bcran/src/tmp/edk2/OvmfPkg/OvmfXen.dsc(...): error F002: Library 
[/home/bcran/src/tmp/edk2/MdePkg/Library/UefiBootServicesTableLib/UefiBootServicesTableLib.inf] 
with constructors has a cycle
                 consumed by 
/home/bcran/src/tmp/edk2/MdePkg/Library/UefiLib/UefiLib.inf
         consumed by 
/home/bcran/src/tmp/edk2/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLibDevicePathProtocol.inf


- Failed -
Build end time: 11:59:25, Apr.14 2020
Build total time: 00:00:02


-- 
Rebecca Cran