Extend test-dlopen-so to also cover cases when built without support

Let's make things more consistent and have all dlopen_xxx() functions
return EOPNOTSUPP on failure and verify this behavior in test-dlopen-so.

src/basic/compress.c

@@ -144,8 +144,8 @@ bool compression_supported(Compression c) {
         return BIT_SET(supported, c);
 }
 
-#if HAVE_XZ
 int dlopen_lzma(void) {
+#if HAVE_XZ
         ELF_NOTE_DLOPEN("lzma",
                         "Support lzma compression in journal and coredump files",
                         COMPRESSION_PRIORITY_XZ,
@@ -160,8 +160,10 @@ int dlopen_lzma(void) {
                         DLSYM_ARG(lzma_stream_buffer_encode),
                         DLSYM_ARG(lzma_lzma_preset),
                         DLSYM_ARG(lzma_stream_decoder));
-}
+#else
+        return -EOPNOTSUPP;
 #endif
+}
 
 int compress_blob_xz(const void *src, uint64_t src_size,
                      void *dst, size_t dst_alloc_size, size_t *dst_size, int level) {
@@ -213,8 +215,8 @@ int compress_blob_xz(const void *src, uint64_t src_size,
 #endif
 }
 
-#if HAVE_LZ4
 int dlopen_lz4(void) {
+#if HAVE_LZ4
         ELF_NOTE_DLOPEN("lz4",
                         "Support lz4 compression in journal and coredump files",
                         COMPRESSION_PRIORITY_LZ4,
@@ -238,8 +240,10 @@ int dlopen_lz4(void) {
                         DLSYM_ARG(LZ4_decompress_safe),
                         DLSYM_ARG(LZ4_decompress_safe_partial),
                         DLSYM_ARG(LZ4_versionNumber));
-}
+#else
+        return -EOPNOTSUPP;
 #endif
+}
 
 int compress_blob_lz4(const void *src, uint64_t src_size,
                       void *dst, size_t dst_alloc_size, size_t *dst_size, int level) {
@@ -278,8 +282,8 @@ int compress_blob_lz4(const void *src, uint64_t src_size,
 #endif
 }
 
-#if HAVE_ZSTD
 int dlopen_zstd(void) {
+#if HAVE_ZSTD
         ELF_NOTE_DLOPEN("zstd",
                         "Support zstd compression in journal and coredump files",
                         COMPRESSION_PRIORITY_ZSTD,
@@ -304,8 +308,10 @@ int dlopen_zstd(void) {
                         DLSYM_ARG(ZSTD_isError),
                         DLSYM_ARG(ZSTD_createDCtx),
                         DLSYM_ARG(ZSTD_createCCtx));
-}
+#else
+        return -EOPNOTSUPP;
 #endif
+}
 
 int compress_blob_zstd(
                 const void *src, uint64_t src_size,

src/basic/compress.h

@@ -62,17 +62,9 @@ int decompress_stream_xz(int fdf, int fdt, uint64_t max_size);
 int decompress_stream_lz4(int fdf, int fdt, uint64_t max_size);
 int decompress_stream_zstd(int fdf, int fdt, uint64_t max_size);
 
-#if HAVE_LZ4
 int dlopen_lz4(void);
-#endif
-
-#if HAVE_ZSTD
 int dlopen_zstd(void);
-#endif
-
-#if HAVE_XZ
 int dlopen_lzma(void);
-#endif
 
 static inline int compress_blob(
                 Compression compression,

src/basic/gcrypt-util.c

@@ -1,11 +1,11 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#if HAVE_GCRYPT
-
 #include <sys/syslog.h>
 
 #include "gcrypt-util.h"
 
+#if HAVE_GCRYPT
+
 static void *gcrypt_dl = NULL;
 
 static DLSYM_PROTOTYPE(gcry_control) = NULL;
@@ -40,8 +40,10 @@ DLSYM_PROTOTYPE(gcry_mpi_sub_ui) = NULL;
 DLSYM_PROTOTYPE(gcry_prime_check) = NULL;
 DLSYM_PROTOTYPE(gcry_randomize) = NULL;
 DLSYM_PROTOTYPE(gcry_strerror) = NULL;
+#endif
 
-static int dlopen_gcrypt(void) {
+int dlopen_gcrypt(void) {
+#if HAVE_GCRYPT
         ELF_NOTE_DLOPEN("gcrypt",
                         "Support for journald forward-sealing",
                         ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED,
@@ -82,9 +84,13 @@ static int dlopen_gcrypt(void) {
                         DLSYM_ARG(gcry_prime_check),
                         DLSYM_ARG(gcry_randomize),
                         DLSYM_ARG(gcry_strerror));
+#else
+        return -EOPNOTSUPP;
+#endif
 }
 
 int initialize_libgcrypt(bool secmem) {
+#if HAVE_GCRYPT
         int r;
 
         r = dlopen_gcrypt();
@@ -105,5 +111,7 @@ int initialize_libgcrypt(bool secmem) {
         sym_gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0);
 
         return 0;
-}
+#else
+        return -EOPNOTSUPP;
 #endif
+}

src/basic/gcrypt-util.h

@@ -4,6 +4,10 @@
 
 #include "forward.h"
 
+int dlopen_gcrypt(void);
+
+int initialize_libgcrypt(bool secmem);
+
 #if HAVE_GCRYPT
 #include <gcrypt.h> /* IWYU pragma: export */
 
@@ -40,8 +44,6 @@ extern DLSYM_PROTOTYPE(gcry_prime_check);
 extern DLSYM_PROTOTYPE(gcry_randomize);
 extern DLSYM_PROTOTYPE(gcry_strerror);
 
-int initialize_libgcrypt(bool secmem);
-
 /* Copied from gcry_md_putc from gcrypt.h due to the need to call the sym_ variant */
 #define sym_gcry_md_putc(h,c)                              \
         do {                                               \