Rewrite FileSearch and improve ScanDirectoryTree.

- FileSearch is now just one function, and it converts the original glob
  into a regex on all platforms rather than relying on native Windows
  pattern matching on there and a complete hack elsewhere.  It now
  supports recursion out of the box rather than manually expanding
  into a full list of directories in multiple call sites.

  - This adds a GCC >= 4.9 dependency due to older versions having
  outright broken <regex>.  MSVC is fine with it.

- ScanDirectoryTree returns the parent entry rather than filling parts
  of it in via reference.  The count is now stored in the entry like it
  was for subdirectories.

- .glsl file search is now done with DoFileSearch.

- IOCTLV_READ_DIR now uses ScanDirectoryTree directly and sorts the
  results after replacements for better determinism.

Source/Core/Core/HW/WiiSaveCrypted.cpp

@@ -67,9 +67,8 @@ void CWiiSaveCrypted::ExportAllSaves()
 	const u32 path_mask = 0x00010000;
 	for (int i = 0; i < 8; ++i)
 	{
-		File::FSTEntry fst_tmp;
 		std::string folder = StringFromFormat("%s/%08x/", title_folder.c_str(), path_mask | i);
-		File::ScanDirectoryTree(folder, fst_tmp);
+		File::FSTEntry fst_tmp = File::ScanDirectoryTree(folder, false);
 
 		for (const File::FSTEntry& entry : fst_tmp.children)
 		{
@@ -627,8 +626,7 @@ void CWiiSaveCrypted::ScanForFiles(const std::string& save_directory, std::vecto
 			file_list.push_back(directories[i]);
 		}
 
-		File::FSTEntry fst_tmp;
-		File::ScanDirectoryTree(directories[i], fst_tmp);
+		File::FSTEntry fst_tmp = File::ScanDirectoryTree(directories[i], false);
 		for (const File::FSTEntry& elem : fst_tmp.children)
 		{
 			if (elem.virtualName != "banner.bin")