Bug 1904543 - Don't add -z defs on Windows builds. r=firefox-build-system-reviewers,ahochheiden

Differential Revision: https://phabricator.services.mozilla.com/D214898

build/moz.configure/flags.configure

@@ -314,6 +314,7 @@ def add_gnu_specific_dso_flags(
         # linked against executables, so we must allow undefined
         # symbols for shared objects in some cases.
         if not use_sanitizer_runtime:
+            if target.os != "WINNT":
                 # Don't allow undefined symbols in libraries
                 ldopts.append("-Wl,-z,defs")