demos: tidy up makefiles, fix warnings

Update makefiles so that consistent patterns are used.  Object files
are compiled from source using an implicit rule (but using our
CFLAGS); for linking, we give an explicit rule.  Ensure that "make
test" works in each subdirectory (even if it does not actually run any
applications).  The top-level demo makefile now works.

The makefiles are not make-agnostic.  e.g. they use the variable $(RM)
in "clean" recipes, which is defined in gnu-make but may not be
defined in others.

Part of #17806

Testing:

  $ cd demo
  $ make test

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22698)

1 files changed, 7 insertions, 4 deletions

diff --git a/demos/smime/smsign2.c b/demos/smime/smsign2.c
index 4e62c6b82c..5ad86f15f8 100644
--- a/demos/smime/smsign2.c
+++ b/demos/smime/smsign2.c
@@ -7,7 +7,7 @@
  * https://www.openssl.org/source/license.html
  */
 
-/* S/MIME signing example: 2 signers. OpenSSL 0.9.9 only */
+/* S/MIME signing example: 2 signers */
 #include <openssl/pem.h>
 #include <openssl/pkcs7.h>
 #include <openssl/err.h>
@@ -30,7 +30,8 @@ int main(int argc, char **argv)
 
     scert = PEM_read_bio_X509(tbio, NULL, 0, NULL);
 
-    BIO_reset(tbio);
+    if (BIO_reset(tbio) < 0)
+        goto err;
 
     skey = PEM_read_bio_PrivateKey(tbio, NULL, 0, NULL);
 
@@ -43,7 +44,8 @@ int main(int argc, char **argv)
 
     scert2 = PEM_read_bio_X509(tbio, NULL, 0, NULL);
 
-    BIO_reset(tbio);
+    if (BIO_reset(tbio) < 0)
+        goto err;
 
     skey2 = PEM_read_bio_PrivateKey(tbio, NULL, 0, NULL);
 
@@ -77,8 +79,9 @@ int main(int argc, char **argv)
     if (!SMIME_write_PKCS7(out, p7, in, PKCS7_STREAM))
         goto err;
 
-    ret = EXIT_SUCCESS;
+    printf("Success\n");
 
+    ret = EXIT_SUCCESS;
  err:
     if (ret != EXIT_SUCCESS) {
         fprintf(stderr, "Error Signing Data\n");