Combine changelog entries for muladdc assembly fix

Combine the changelog entries for the memory constraints fix on
aarch64 and amd64, since these are essentially fixing the same
issue.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/ChangeLog.d/muladdc-memory.txt b/ChangeLog.d/muladdc-memory.txt
new file mode 100644
index 0000000..218be5a
--- /dev/null
+++ b/ChangeLog.d/muladdc-memory.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Fix missing constraints on x86_64 and aarch64 assembly code
+     for bignum multiplication that broke some bignum operations with
+     (at least) Clang 12.
+     Fixes #4116, #4786, #4917, #4962.