* fix some macro expansion issues
* add some pp tests in tests/pp
* improved tcc -E output for better diff'ability
* remove -dD feature (quirky code, exotic feature,
  didn't work well)

Based partially on ideas / researches from PipCet

Some issues remain with VA_ARGS macros (if used in a
rather tricky way).

Also, to keep it simple, the pp doesn't automtically
add any extra spaces to separate tokens which otherwise
would form wrong tokens if re-read from tcc -E output
(such as '+' '=')  GCC does that, other compilers don't.

 * cleanups
  - #line 01 "file" / # 01 "file" processing
  - #pragma comment(lib,"foo")
  - tcc -E: forward some pragmas to output (pack, comment(lib))
  - fix macro parameter list parsing mess from
    a3fc5434
    a715d714
    (some coffee might help, next time ;)
  - introduce TOK_PPSTR - to have character constants as
    written in the file (similar to TOK_PPNUM)
  - allow '\' appear in macros
  - new functions begin/end_macro to:
      - fix switching macro levels during expansion
      - allow unget_tok to unget more than one tok
  - slight speedup by using bitflags in isidnum_table

Also:
  - x86_64.c : fix decl after statements
  - i386-gen,c : fix a vstack leak with VLA on windows
  - configure/Makefile : build on windows (MSYS) was broken
  - tcc_warning: fflush stderr to keep output order (win32)