Preserve errno on dlopen

For the same reasons as in the previous commit we must preserve errno
across dlopen calls. Some implementations (e.g. solaris) do not preserve
errno even on a successful dlopen call.

Fixes #6953
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7680)

(cherry picked from commit 3cb4e7dc1cf92022f62b9bbdd59695885a1265ff)

crypto/dso/dso_dlfcn.c

@@ -17,6 +17,7 @@
 #endif
 
 #include "dso_locl.h"
+#include "e_os.h"
 
 #ifdef DSO_DLFCN
 
@@ -99,6 +100,7 @@ static int dlfcn_load(DSO *dso)
     /* See applicable comments in dso_dl.c */
     char *filename = DSO_convert_filename(dso, NULL);
     int flags = DLOPEN_FLAG;
+    int saveerrno = get_last_sys_error();
 
     if (filename == NULL) {
         DSOerr(DSO_F_DLFCN_LOAD, DSO_R_NO_FILENAME);
@@ -118,6 +120,11 @@ static int dlfcn_load(DSO *dso)
         ERR_add_error_data(4, "filename(", filename, "): ", dlerror());
         goto err;
     }
+    /*
+     * Some dlopen() implementations (e.g. solaris) do no preserve errno, even
+     * on a successful call.
+     */
+    set_sys_error(saveerrno);
     if (!sk_void_push(dso->meth_data, (char *)ptr)) {
         DSOerr(DSO_F_DLFCN_LOAD, DSO_R_STACK_ERROR);
         goto err;