Add Changelog

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/fix-rsaalt-test-guards.txt b/ChangeLog.d/fix-rsaalt-test-guards.txt
new file mode 100644
index 0000000..f4f39c9
--- /dev/null
+++ b/ChangeLog.d/fix-rsaalt-test-guards.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix compile error where MBEDTLS_RSA_C and MBEDTLS_X509_CRT_WRITE_C are
+     defined, but MBEDTLS_PK_RSA_ALT_SUPPORT is not defined. Fixes #3174.