CMake: support "make ssl-opt" to just build what ssl-opt.sh needs

This also suffices for compat.sh.

Include the sample programs in this build. They aren't tested by ssl-opt.sh
yet, but they soon will be.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/programs/CMakeLists.txt b/programs/CMakeLists.txt
index aaf93ba..e031544 100644
--- a/programs/CMakeLists.txt
+++ b/programs/CMakeLists.txt
@@ -1,6 +1,9 @@
 set(programs_target "${MBEDTLS_TARGET_PREFIX}programs")
 add_custom_target(${programs_target})
 
+set(ssl_opt_target "${MBEDTLS_TARGET_PREFIX}ssl-opt")
+add_custom_target(${ssl_opt_target})
+
 add_subdirectory(aes)
 add_subdirectory(cipher)
 if (NOT WIN32)