Fix missing-prototype errors in sample programs

Signed-off-by: Michael Schuster <michael@schuster.ms>
diff --git a/programs/test/selftest.c b/programs/test/selftest.c
index 043209b..e72386f 100644
--- a/programs/test/selftest.c
+++ b/programs/test/selftest.c
@@ -241,7 +241,7 @@
 }
 #endif
 
-int mbedtls_entropy_self_test_wrapper(int verbose)
+static int mbedtls_entropy_self_test_wrapper(int verbose)
 {
 #if defined(MBEDTLS_ENTROPY_NV_SEED) && !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
     create_entropy_seed_file();
@@ -252,7 +252,7 @@
 
 #if defined(MBEDTLS_SELF_TEST)
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
-int mbedtls_memory_buffer_alloc_free_and_self_test(int verbose)
+static int mbedtls_memory_buffer_alloc_free_and_self_test(int verbose)
 {
     if (verbose != 0) {
 #if defined(MBEDTLS_MEMORY_DEBUG)