util: Work around libstdc++ create_directories issue

Work around libstdc++ issue [PR101510] with create_directories where the
leaf already exists as a symlink. Fixes #24257, introduced by the switch
to `std::filesystem`. It is meant to be more thorough than #24266, which
only worked around one instance of the problem.

The issue was fixed upstream in
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=124eaa50e0a34f5f89572c1aa812c50979da58fc,
but unfortunately we'll have to carry a fix for it for a while.

This introduces a function `fs::create_directories` which wraps
`std::filesystem::create_directories`. This allows easiliy reverting the
workaround when it is no longer necessary.

src/fs.h

@@ -140,6 +140,28 @@ static inline path PathFromString(const std::string& string)
     return std::filesystem::path(string);
 #endif
 }
+
+/**
+ * Create directory (and if necessary its parents), unless the leaf directory
+ * already exists or is a symlink to an existing directory.
+ * This is a temporary workaround for an issue in libstdc++ that has been fixed
+ * upstream [PR101510].
+ */
+static inline bool create_directories(const std::filesystem::path& p)
+{
+    if (std::filesystem::is_symlink(p) && std::filesystem::is_directory(p)) {
+        return false;
+    }
+    return std::filesystem::create_directories(p);
+}
+
+/**
+ * This variant is not used. Delete it to prevent it from accidentally working
+ * around the workaround. If it is needed, add a workaround in the same pattern
+ * as above.
+ */
+bool create_directories(const std::filesystem::path& p, std::error_code& ec) = delete;
+
 } // namespace fs
 
 /** Bridge operations to C stdio */

src/test/dbwrapper_tests.cpp

@@ -203,7 +203,7 @@ BOOST_AUTO_TEST_CASE(existing_data_no_obfuscate)
 {
     // We're going to share this fs::path between two wrappers
     fs::path ph = m_args.GetDataDirBase() / "existing_data_no_obfuscate";
-    create_directories(ph);
+    fs::create_directories(ph);
 
     // Set up a non-obfuscated wrapper to write some initial data.
     std::unique_ptr<CDBWrapper> dbw = std::make_unique<CDBWrapper>(ph, (1 << 10), false, false, false);
@@ -244,7 +244,7 @@ BOOST_AUTO_TEST_CASE(existing_data_reindex)
 {
     // We're going to share this fs::path between two wrappers
     fs::path ph = m_args.GetDataDirBase() / "existing_data_reindex";
-    create_directories(ph);
+    fs::create_directories(ph);
 
     // Set up a non-obfuscated wrapper to write some initial data.
     std::unique_ptr<CDBWrapper> dbw = std::make_unique<CDBWrapper>(ph, (1 << 10), false, false, false);