Explain why we check that a certain feature is enabled

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 27aeb8c..e4ab85c 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2625,6 +2625,7 @@
     scripts/config.py -w full_config.h full
     echo '#error "MBEDTLS_CONFIG_FILE is not working"' >"$CONFIG_H"
     make CFLAGS="-I '$PWD' -DMBEDTLS_CONFIG_FILE='\"full_config.h\"'"
+    # Make sure this feature is enabled. We'll disable it in the next phase.
     programs/test/query_compile_time_config MBEDTLS_NIST_KW_C
     make clean
 
@@ -2644,6 +2645,7 @@
     cp "$CRYPTO_CONFIG_H" psa_test_config.h
     echo '#error "MBEDTLS_PSA_CRYPTO_CONFIG_FILE is not working"' >"$CRYPTO_CONFIG_H"
     make CFLAGS="-I '$PWD' -DMBEDTLS_PSA_CRYPTO_CONFIG_FILE='\"psa_test_config.h\"'"
+    # Make sure this feature is enabled. We'll disable it in the next phase.
     programs/test/query_compile_time_config MBEDTLS_CMAC_C
     make clean