4 tests from spec/testsuite/conversions.wast and spec/testsuite/simd_conversions.wast fail on ppc64le

[rathann]

When running binaryen 129 testsuite on ppc64le, I get the following 4 failures:

/builddir/build/BUILD/binaryen-129-build/binaryen-version_129/redhat-linux-build/bin/wasm-shell /builddir/build/BUILD/binaryen-129-build/binaryen-version_129/test/spec/testsuite/simd_conversions.wast
...
485 CHECKING [line: 561]
expected arithmetic f64, got nan:0x4000000000000
486 CHECKING [line: 563]
expected arithmetic f64, got -nan:0x4000000000000

and

/builddir/build/BUILD/binaryen-129-build/binaryen-version_129/redhat-linux-build/bin/wasm-shell /builddir/build/BUILD/binaryen-129-build/binaryen-version_129/test/spec/testsuite/simd_conversions.wast
...
14 CHECKING [line: 63]
expected arithmetic f64, got i32x4 0x00000000 0x7ff40000 0x00000000 0x7ff40000 at lane 0
15 CHECKING [line: 67]
expected arithmetic f64, got i32x4 0x00000000 0xfff40000 0x00000000 0xfff40000 at lane 0

This is a regressions between 126 and 129, but I haven't tested 127 or 128 yet.

[rathann]

Looks like #8528 and #8472 are related to this.

[kripken]

cc @stevenfontanella based on the linked issues