unsorted adjustments

- configure
  * use aarch64 instead of arm64

- Makefile
  * rename the custom include file to "config-extra.mak"
  * Also avoid "rm -r /*" if $(tccdir) is empty

- pp/Makefile
  * fix .expect generation with gcc

- tcc.h
  * cleanup #defines for _MSC_VER

- tccgen.c:
  * fix const-propagation for &,|
  * fix anonymous named struct (ms-extension) and enable
    -fms-extension by default

- i386-gen.c
  * clear VT_DEFSIGN

- x86_64-gen.c/win64:
  * fix passing structs in registers
  * fix alloca (need to keep "func_scratch" below each alloca area on stack)
    (This allows to compile a working gnu-make on win64)

- tccpp.c
  * alternative approach to 37999a4fbf
    This is to avoid some slowdown with ## token pasting.
  * get_tok_str() : return <eof> for TOK_EOF
  * -funsigned-char: apply to "string" literals as well

- tccpe/tools.c: -impdef: support both 32 and 64 bit dlls anyway

tcctools.c

@@ -363,9 +363,8 @@ usage:
     ret = tcc_get_dllexports(file, &p);
     if (ret || !p) {
         fprintf(stderr, "tcc: impdef: %s '%s'\n",
-            ret == 32 ? "can't read symbols from 32bit" :
-            ret == 64 ? "can't read symbols from 64bit" :
             ret == -1 ? "can't find file" :
+            ret ==  1 ? "can't read symbols" :
             ret ==  0 ? "no symbols found in" :
             "unknown file type", file);
         ret = 1;