for floats (currently only). On x86_64 uses built-in fp
constants (in libtcc1.c) to avoid multiple anonymous
instances.
Also: win32/i386: use __alloca for big struct stack store
- use new function int tok_alloc_const(const char*);
- change alloca86.S to preserve EDX
tccelf.c: fix a warning with 'roinf_use'