Add changelog entry for build error fixes

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/build-without-sha.txt b/ChangeLog.d/build-without-sha.txt
new file mode 100644
index 0000000..78ba276
--- /dev/null
+++ b/ChangeLog.d/build-without-sha.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix the build when no SHA2 module is included. Fixes #4930.
+   * Fix the build when only the bignum module is included. Fixes #4929.