libtcc: new LIBTCCAPI tcc_set_options(TCCState*, const char*str)

This replaces       -> use instead:
-----------------------------------
- tcc_set_linker    -> tcc_set_options(s, "-Wl,...");
- tcc_set_warning   -> tcc_set_options(s, "-W...");
- tcc_enable_debug  -> tcc_set_options(s, "-g");

parse_args is moved to libtcc.c (now tcc_parse_args).

Also some cleanups:
- reorder TCCState members
- add some comments here and there
- do not use argv's directly, make string copies
- use const char* in tcc_set_linker
- tccpe: use fd instead of fp

tested with -D MEM_DEBUG: 0 bytes left

Changelog

@@ -4,7 +4,8 @@ User interface:
 - -MD/-MF (automatically generate dependencies for make)
 - -pthread option (same as -D_REENTRANT -lpthread) (Henry Kroll III)
 - -m32/-m64 to re-exec cross compiler (Henry Kroll III)
-- Mimic all GNU -option forms supported by ld (Kirill Smelkov)
+- -Wl, Mimic all GNU -option forms supported by ld (Kirill Smelkov)
+- new LIBTCCAPI tcc_set_options() (grischka)
 
 Platforms:
 - Many improvements for x86-64 target (Shinichiro Hamaji, Michael Matz, grischka)