tests/Makefile: fix out-of-tree build issues

Also:

- win64: align(16) MEM_DEBUG user memory
  on win64 the struct jmp_buf in the TCCState structure which we
  allocate by tcc_malloc needs alignment 16 because the msvcrt
  setjmp uses MMX instructions.

- libtcc_test.c: win32/64 need __attribute__((dllimport)) for
  extern data objects

- tcctest.c: exclude stuff that gcc does not compile
  except for relocation_test() the other issues are mostly ASM
  related.  We should probably check GCC versions but I have
  no idea which mingw/gcc versions support what and which don't.

- lib/Makefile: use tcc to compile libtcc1.a (except on arm
  which needs arm-asm

- generate and use SYM@PLT for plt addresses
- get rid of patch_dynsym_undef hack (no idea what it did on FreeBSD)
- use sym_attrs instead of symtab_to_dynsym
- special case for function pointers into .so on i386
- libtcc_test: test tcc_add_symbol with data object
- move target specicic code to *-link.c files
- add R_XXX_RELATIVE (needed for PE)

* 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
    a3fc54345949535524d01319e1ca6378b7c2c201
    a715d7143d9d17da17e67fec6af1c01409a71a31
    (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)

    ------------ libtest ------------
    ./libtcc_test lib_path=..
    <string>:11: warning: implicit declaration of function 'printf'
    <string>:13: warning: implicit declaration of function 'add'
    ------------ test3 ------------
    tcctest.c:1982: warning: implicit declaration of function 'putchar'
    tcctest.c:2133: warning: implicit declaration of function 'strlen'

We are now compatible with the 0.9,25 version though.  A special
value for the second (ptr) argument is used to get the simple
behavior as with the 0.9.24 version.