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, 1 insertions, 4 deletions

diff --git a/demos/cipher/ariacbc.c b/demos/cipher/ariacbc.c
index f9898e12c7..de84d995ec 100644
--- a/demos/cipher/ariacbc.c
+++ b/demos/cipher/ariacbc.c
@@ -58,9 +58,7 @@ int aria_cbc_encrypt(void)
     EVP_CIPHER_CTX *ctx;
     EVP_CIPHER *cipher = NULL;
     int outlen, tmplen;
-    size_t cbc_ivlen = sizeof(cbc_iv);
     unsigned char outbuf[1024];
-    unsigned char outtag[16];
 
     printf("ARIA CBC Encrypt:\n");
     printf("Plaintext:\n");
@@ -115,8 +113,7 @@ int aria_cbc_decrypt(void)
     int ret = 0;
     EVP_CIPHER_CTX *ctx;
     EVP_CIPHER *cipher = NULL;
-    int outlen, tmplen, rv;
-    size_t cbc_ivlen = sizeof(cbc_iv);
+    int outlen, tmplen;
     unsigned char outbuf[1024];
 
     printf("ARIA CBC Decrypt:\n");