Add dependency of mbedtls_config on generated config check headers

Fix the build of libmbedx509 when generated files are not already present.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/Makefile b/library/Makefile
index a0b6d6e..9085ab4 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -346,6 +346,8 @@
 	echo "  Gen   $(GENERATED_CONFIG_CHECK_FILES)"
 	$(PYTHON) ../scripts/generate_config_checks.py
 
+mbedtls_config.o: $(GENERATED_CONFIG_CHECK_FILES)
+
 TF_PSA_CRYPTO_GENERATED_CONFIG_CHECK_FILES = $(shell $(PYTHON) \
 	$(TF_PSA_CRYPTO_CORE_PATH)/../scripts/generate_config_checks.py \
 	--list $(TF_PSA_CRYPTO_CORE_PATH))