Update testsuite; fix conversion errors

[binji]

The interpreter and wasm2c were incorrectly handling some float-to-int
conversions. For clarity, the wasm2c implementations of these
conversions now matches the implementation in interp-math.h more closely
(e.g. the numeric ranges are written as x >= min && x <= max in both
cases).

Quite a few wasm2c tests were previously being skipped, since wasm2c
doesn't currently support multi-value; it's better instead to duplicate
the tests here and disable the parts that are not supported so we don't
lose test coverage.

[binji]

Thanks for double-checking the bounds! I had to think about them a bit to convince myself these are the correct values, but I think they are. For the 8 cases, (s32/u32/s64/u64 <- f32/f64), if we consider which values should be bounds if we had infinite floating-point precision, we would have the following (where _MAX values are the maximum value that is representable type):

to	from	min (excl.)	max (excl.)
s32	f32 or f64	INT32_MIN - 1	INT32_MAX + 1
u32	f32 or f64	-1	UINT32_MAX + 1
s64	f32 or f64	INT64_MIN - 1	INT64_MAX + 1
u64	f32 or f64	-1	UINT64_MAX + 1

Now we have to consider which of these values are representable as f32 or f64. The values that had to be truncated are in bold:

value	int	f32	f64
INT32_MIN - 1	-2147483649	-2147483648.0	-2147483649.0
INT32_MAX + 1	2147483648	2147483648	2147483648
UINT32_MAX + 1	4294967296	4294967296	4294967296
INT64_MIN - 1	-9223372036854775809	-9223372036854775808.0	-9223372036854775808.0
INT64_MAX + 1	9223372036854775808	9223372036854775808	9223372036854775808
UINT64_MAX + 1	18446744073709551616	18446744073709551616.0	18446744073709551616.0

And finally, we can determine the bounds, where the ranges that had to be modified are in bold:

instr	to	from	valid bounds
i32.trunc_f32_s	s32	f32	-2147483648.f <= x < 2147483648.f
i32.trunc_f64_s	s32	f64	-2147483649.0 < x < 2147483648.0
i32.trunc_f32_u	u32	f32	-1.f < x < 4294967296.f
i32.trunc_f64_u	u32	f64	-1.0 < x < 4294967296.0
i64.trunc_f32_s	s64	f32	-9223372036854775808.f <= x < 9223372036854775808.f
i64.trunc_f64_s	s64	f64	-9223372036854775808.f <= x < 9223372036854775808.f
i64.trunc_f32_u	u64	f32	-1.f < x < 18446744073709551616.f
i64.trunc_f64_u	u64	f64	-1.0 < x < 18446744073709551616.0