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/DolphinWX/InputConfigDiag.cpp

@@ -172,18 +172,14 @@ void InputConfigDialog::UpdateProfileComboBox()
 	pname += PROFILES_PATH;
 	pname += m_config.profile_name;
 
-	CFileSearch::XStringVector exts;
-	exts.push_back("*.ini");
-	CFileSearch::XStringVector dirs;
-	dirs.push_back(pname);
-	CFileSearch cfs(exts, dirs);
-	const CFileSearch::XStringVector& sv = cfs.GetFileNames();
+	std::vector<std::string> sv = DoFileSearch({"*.ini"}, {pname});
 
 	wxArrayString strs;
-	for (auto si = sv.cbegin(); si != sv.cend(); ++si)
+	for (const std::string& filename : sv)
 	{
-		std::string str(si->begin() + si->find_last_of('/') + 1 , si->end() - 4) ;
-		strs.push_back(StrToWxStr(str));
+		std::string base;
+		SplitPath(filename, nullptr, &base, nullptr);
+		strs.push_back(StrToWxStr(base));
 	}
 
 	for (GamepadPage* page : m_padpages)