more minor fixes

more minor fixes

* tccgen: re-allow long double constants for x87 cross
  sizeof (long double) may be 12 or 16 depending on host platform
  (i386/x86_64 on unix/windows).
  Except that it's 8 if the host is on windows and not gcc
  was used to compile tcc.

* win64: fix builtin_va_start after VT_REF removal
  See also a8b83ce43a95fa519dacfe7690a3a0098af7909c

* tcctest.c: remove outdated limitation for ll-bitfield test
  It always worked, there is no reason why it should not work
  in future.

* libtcc1.c: exclude long double conversion on ARM

* Makefile: remove CFLAGS from link recipes

* lib/Makefile: use target DEFINES as passed from main Makefile

* lib/armflush.c lib/va_list.c: factor out from libtcc1.c

* arm-gen.c: disable "depreciated" warnings for now