cranelift: Add big and little endian memory accesses to interpreter (#5893)

* Added `mem_flags` parameter to `State::checked_{load,store}` as the means
for determining the endianness, typically derived from an instruction.

* Added `native_endianness` property to `InterpreterState` as fallback when
determining endianness, such as in cases where there are no memory flags
avaiable or set.

* Added `to_be` and `to_le` methods to `DataValue`.

* Added `AtomicCas` and `AtomicRmw` to list of instructions with retrievable
memory flags for `InstructionData::memflags`.

* Enabled `atomic-{cas,rmw}-subword-{big,little}.clif` for interpreter run
tests.

cranelift/filetests/filetests/runtests/atomic-cas-subword-big.clif

@@ -1,3 +1,4 @@
+test interpret
 test run
 target s390x
 

cranelift/filetests/filetests/runtests/atomic-cas-subword-little.clif

@@ -1,3 +1,4 @@
+test interpret
 test run
 target s390x
 target aarch64

cranelift/filetests/filetests/runtests/atomic-rmw-subword-big.clif

@@ -1,3 +1,4 @@
+test interpret
 test run
 target s390x
 target s390x has_mie2
@@ -431,10 +432,10 @@ block0(v0: i32, v1: i64, v2: i16):
     v6 = load.i32 big v3
     return v6
 }
-; run: %atomic_rmw_xchg_little_i16(0x12345678, 0, 0x1111) == 0x11115678
-; run: %atomic_rmw_xchg_little_i16(0x12345678, 0, 0xffff) == 0xffff5678
-; run: %atomic_rmw_xchg_little_i16(0x12345678, 2, 0x1111) == 0x12341111
-; run: %atomic_rmw_xchg_little_i16(0x12345678, 2, 0xffff) == 0x1234ffff
+; run: %atomic_rmw_xchg_big_i16(0x12345678, 0, 0x1111) == 0x11115678
+; run: %atomic_rmw_xchg_big_i16(0x12345678, 0, 0xffff) == 0xffff5678
+; run: %atomic_rmw_xchg_big_i16(0x12345678, 2, 0x1111) == 0x12341111
+; run: %atomic_rmw_xchg_big_i16(0x12345678, 2, 0xffff) == 0x1234ffff
 
 
 function %atomic_rmw_xchg_big_i8(i32, i64, i8) -> i32 {

cranelift/filetests/filetests/runtests/atomic-rmw-subword-little.clif

@@ -1,3 +1,4 @@
+test interpret
 test run
 target s390x
 target s390x has_mie2