CMake: fix build with 3rdparty module enabled through a custom config

Fixes #8165

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/fix-cmake-3rdparty-custom-config.txt b/ChangeLog.d/fix-cmake-3rdparty-custom-config.txt
new file mode 100644
index 0000000..ec543aa
--- /dev/null
+++ b/ChangeLog.d/fix-cmake-3rdparty-custom-config.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix the build with CMake when Everest or P256-m is enabled through
+     a user configuration file or the compiler command line. Fixes #8165.