Revert "update static void parse_number()"

Revert "update static void parse_number()"

because:
- Constructing fp numbers isn't quite trivial
- 3 additional calls to strchr per number is noticeable slow

Also: exclude abitest.c:ret_longdouble_test2 on _WIN32
for mixed gcc/tcc scenario

test case:
- make -k test (on win32):
  -2.120000 0.500000 23000000000.000000
  +2.120000 0.500000 22999999999.999996
  ...
  ret_longdouble_test2... failure

This reverts 857f7dbfa65179e6690dbee7ab915fb4458cee11
and deaee6c2496ecb25858290405fef8ef79aece979