Add support for Xcode 12.3 (12C33)

Author: shahmishal

utils/build-script

@@ -56,6 +56,7 @@ _SUPPORTED_XCODE_BUILDS = [
     ("12.2 beta 3", "12B5035g"),
     ("12.2 Release Candidate", "12B5044c"),
     ("12.2", "12B45b"),
+    ("12.3", "12C33"),
 ]
 
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