Add Changelog for Arm compile fix

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/fix_arm_compile_erorr.txt b/ChangeLog.d/fix_arm_compile_erorr.txt
new file mode 100644
index 0000000..28c1d45
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+++ b/ChangeLog.d/fix_arm_compile_erorr.txt
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+Bugfix
+    * Fix a build error when compiling the bignum module for some Arm platforms.
+      Fixes #6089, #6124, #6217.