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/Common/FileUtil.h

@@ -107,9 +107,8 @@ bool Copy(const std::string &srcFilename, const std::string &destFilename);
 // creates an empty file filename, returns true on success
 bool CreateEmptyFile(const std::string &filename);
 
-// Scans the directory tree gets, starting from _Directory and adds the
-// results into parentEntry. Returns the number of files+directories found
-u32 ScanDirectoryTree(const std::string &directory, FSTEntry& parentEntry);
+// Recursive or non-recursive list of files under directory.
+FSTEntry ScanDirectoryTree(const std::string &directory, bool recursive);
 
 // deletes the given directory and anything under it. Returns true on success.
 bool DeleteDirRecursively(const std::string &directory);