Add an MSVC branch to MONO_ALWAYS_INLINE.
Only require mono_arch_is_soft_float () to be defined when needed.

Now, only ports that define MONO_ARCH_SOFT_FLOAT_FALLBACK have to
provide this function. For ports that don't define this, a default
function is provided that returns FALSE.
Fix a #define style issue in mini.c.

Introduced in d4016989729bd58274c03d7b8ed9495bfbfef82f.