tccgen: fix long long -> char/short cast

This was causing assembler bugs in a tcc compiled by itself
at i386-asm.c:352 when ExprValue.v was changed to uint64_t:

    if (op->e.v == (int8_t)op->e.v)
        op->type |= OP_IM8S;

A general test case:

    #include <stdio.h>
    int main(int argc, char **argv)
    {
        long long ll = 4000;
        int i = (char)ll;
        printf("%d\n", i);
        return 0;
    }

Output was "4000", now "-96".

Also: add "asmtest2" as asmtest with tcc compiled by itself

tccgen.c

@@ -1948,7 +1948,10 @@ static void force_charshort_cast(int t)
         vpushi((1 << bits) - 1);
         gen_op('&');
     } else {
-        bits = 32 - bits;
+        if ((vtop->type.t & VT_BTYPE) == VT_LLONG)
+            bits = 64 - bits;
+        else
+            bits = 32 - bits;
         vpushi(bits);
         gen_op(TOK_SHL);
         /* result must be signed or the SAR is converted to an SHL