Debug dln load errors

We're currently getting occasional segfaults when failing to load
encoding files. The segfault is preventing us from seeing the raised
error message, so this printing will let us see it in the logs instead.

Author: composerinteralia

dln.c

@@ -403,8 +403,10 @@ dln_open(const char *file)
             if (dln_disable_dlclose()) {
                 /* dlclose() segfaults */
                 if (libruby_name) {
+                    fprintf(stderr, "DLOPEN ERROR: (fatal) linked to incompatible %s - %s\n", libruby_name, file);
                     dln_fatalerror("linked to incompatible %s - %s", libruby_name, file);
                 }
+                fprintf(stderr, "DLOPEN ERROR: (fatal) %s - %s\n", incompatible, file);
                 dln_fatalerror("%s - %s", incompatible, file);
             }
             else {
@@ -416,6 +418,7 @@ dln_open(const char *file)
                 }
                 dlclose(handle);
                 if (libruby_name) {
+                    fprintf(stderr, "DLOPEN ERROR: linked to incompatible %s - %s\n", libruby_name, file);
                     dln_loaderror("linked to incompatible %s - %s", libruby_name, file);
                 }
                 error = incompatible;
@@ -429,6 +432,7 @@ dln_open(const char *file)
     return handle;
 
   failed:
+    fprintf(stderr, "DLOPEN ERROR: %s - %s\n", error, file);
     dln_loaderror("%s - %s", error, file);
 }
 
@@ -456,6 +460,7 @@ dln_sym_func(void *handle, const char *symbol)
         const size_t errlen = strlen(error = dln_strerror()) + 1;
         error = memcpy(ALLOCA_N(char, errlen), error, errlen);
 #endif
+        fprintf(stderr, "DLOPEN ERROR: (dln_sym_func) %s - %s\n", error, symbol);
         dln_loaderror("%s - %s", error, symbol);
     }
     return (uintptr_t)func;
@@ -513,6 +518,7 @@ dln_load_and_init(const char *file, const char *init_fct_name)
     abi_version_number binary_abi_version =
         dln_sym_callable(abi_version_number, (void), handle, EXTERNAL_PREFIX "ruby_abi_version")();
     if (binary_abi_version != RUBY_ABI_VERSION && abi_check_enabled_p()) {
+        fprintf(stderr, "DLOPEN ERROR: incompatible ABI version of binary - %s\n", file);
         dln_loaderror("incompatible ABI version of binary - %s", file);
     }
 #endif