test: Check error for non-existent directory symlink #24432

Add a test for the case where the symlink points to a non-existing directory. This confirms the behaviour is identical to the one in v22.0 (using boost):

 node0 stderr ************************
EXCEPTION: N5boost10filesystem16filesystem_errorE       
boost::filesystem::create_directory: File exists: "/tmp/bitcoin_func_test_jozyx4wp/node0/regtest/blocks"       
bitcoin in AppInit() 

The unit test fails, due to a bug in libc++11 and lower:

error: in "fs_tests/create_directories": exception fs::filesystem_error expected but not raised

I've commented out the failing test for now

Prefer to actually workaround the bug...? Can't we easily check for it and error on our own?

It might be possible, but this can be done in a follow-up

Well, I can't reproduce the bug (w/ Clang and libc++ 11.0 or 11.1), but this should workaround it:

diff --git a/src/fs.h b/src/fs.h
index 00b786453c4..c4cd5cd2a28 100644
--- a/src/fs.h
+++ b/src/fs.h
@@ -13,6 +13,7 @@
 #include <ios>
 #include <ostream>
 #include <string>
+#include <system_error>
 #include <utility>
 
 /** Filesystem operations and types */
@@ -149,8 +150,12 @@ static inline path PathFromString(const std::string& string)
  */
 static inline bool create_directories(const std::filesystem::path& p)
 {
-    if (std::filesystem::is_symlink(p) && std::filesystem::is_directory(p)) {
-        return false;
+    if (std::filesystem::is_symlink(p)) {
+        if (std::filesystem::is_directory(p)) {
+            return false;
+        } else if (!std::filesystem::exists(p)) {
+            throw std::filesystem::filesystem_error("cannot create directories", p, std::make_error_code(std::errc::not_a_directory));
+        }
     }
     return std::filesystem::create_directories(p);
 }