python3.9 changed/fixed codec.register behavior to always replace
hyphen with underscore for passed in codec names:

https://bugs.python.org/issue37751

So the custom Ucs2Search needs to be adapted to handle 'ucs_2' in
addition to existing 'ucs-2' for back compat.

This fixes test failures on python3.9, example:

======================================================================
FAIL: testUtf16InUniFile (CheckUnicodeSourceFiles.Tests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/builddir/build/BUILD/edk2-edk2-stable202002/BaseTools/Source/Python/AutoGen/UniClassObject.py", line 375, in PreProcess
FileIn = UniFileClassObject.OpenUniFile(LongFilePath(File.Path))
File "/builddir/build/BUILD/edk2-edk2-stable202002/BaseTools/Source/Python/AutoGen/UniClassObject.py", line 303, in OpenUniFile
UniFileClassObject.VerifyUcs2Data(FileIn, FileName, Encoding)
File "/builddir/build/BUILD/edk2-edk2-stable202002/BaseTools/Source/Python/AutoGen/UniClassObject.py", line 312, in VerifyUcs2Data
Ucs2Info = codecs.lookup('ucs-2')
LookupError: unknown encoding: ucs-2

Signed-off-by: Cole Robinson <crobinso@...>
---
BaseTools/Source/Python/AutoGen/UniClassObject.py | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/BaseTools/Source/Python/AutoGen/UniClassObject.py b/BaseTools/Source/Python/AutoGen/UniClassObject.py
index b2895f7e5c..883c2356e0 100644
--- a/BaseTools/Source/Python/AutoGen/UniClassObject.py
+++ b/BaseTools/Source/Python/AutoGen/UniClassObject.py
@@ -152,7 +152,7 @@ class Ucs2Codec(codecs.Codec):

TheUcs2Codec = Ucs2Codec()
def Ucs2Search(name):
- if name == 'ucs-2':
+ if name in ['ucs-2', 'ucs_2']:
return codecs.CodecInfo(
name=name,
encode=TheUcs2Codec.encode,
--
2.26.2