misc. fixes

- tccgen: error out for cast to void, as in
      void foo(void) { return 1; }
  This avoids an assertion failure in x86_64-gen.c, also.
  also fix tests2/03_struct.c accordingly

- Error: "memory full" - be more specific

- Makefiles: remove circular dependencies, lookup tcctest.c from VPATH

- tcc.h: cleanup lib, include, crt and libgcc search paths"
  avoid duplication or trailing slashes with no CONFIG_MULTIARCHDIR
  (as from 9382d6f1a0)

- tcc.h: remove ";{B}" from PE search path
  in ce5e12c2f9 James Lyon wrote:
  "... I'm not sure this is the right way to fix this problem."
  And the answer is: No, please. (copying libtcc1.a for tests instead)

- win32/build_tcc.bat: do not move away a versioned file

tccpp.c

@@ -197,7 +197,7 @@ static TokenSym *tok_alloc_new(TokenSym **pts, const char *str, int len)
     int i;
 
     if (tok_ident >= SYM_FIRST_ANOM) 
-        tcc_error("memory full");
+        tcc_error("memory full (symbols)");
 
     /* expand token table if needed */
     i = tok_ident - TOK_IDENT;
@@ -1528,7 +1528,7 @@ include_done:
         c = (define_find(tok) != 0) ^ c;
     do_if:
         if (s1->ifdef_stack_ptr >= s1->ifdef_stack + IFDEF_STACK_SIZE)
-            tcc_error("memory full");
+            tcc_error("memory full (ifdef)");
         *s1->ifdef_stack_ptr++ = c;
         goto test_skip;
     case TOK_ELSE: