Fix command injection on PDB download (#16966)

* Fix r_sys_mkdirp with absolute path on Windows
* Fix build with --with-openssl
* Use RBuffer in r_socket_http_answer()
* r_socket_http_answer: Fix read for big responses
* Implement r_str_escape_sh()
* Cleanup r_socket_connect() on Windows
* Fix socket being created without a protocol
* Fix socket connect with SSL ##socket
* Use select() in r_socket_ready()
* Fix read failing if received only protocol answer
* Fix double-free
* r_socket_http_get: Fail if req. SSL with no support
* Follow redirects in r_socket_http_answer()
* Fix r_socket_http_get result length with R2_CURL=1
* Also follow redirects
* Avoid using curl for downloading PDBs
* Use r_socket_http_get() on UNIXs
* Use WinINet API on Windows for r_socket_http_get()
* Fix command injection
* Fix r_sys_cmd_str_full output for binary data
* Validate GUID on PDB download
* Pass depth to socket_http_get_recursive()
* Remove 'r_' and '__' from static function names
* Fix is_valid_guid
* Fix for comments