Add filetests for fcvt_from_sint.f32x4

Add portions of filetests simd-conversion-legalize.clif and simd-conversion-run.clif
that test fcvt_from_sint.f32x4

cranelift/filetests/filetests/isa/x64/simd-conversion-run.clif

@@ -0,0 +1,25 @@
+test run
+set enable_simd
+target x86_64
+feature "experimental_x64"
+
+function %fcvt_from_sint() -> b1 {
+block0:
+    v0 = vconst.i32x4 [-1 0 1 123456789]
+    v1 = fcvt_from_sint.f32x4 v0
+
+    v2 = vconst.f32x4 [-0x1.0 0.0 0x1.0 0x75bcd18.0] ; 123456789 rounds to 123456792.0, an error of 3
+    v3 = fcmp eq v1, v2
+    v4 = vall_true v3
+    return v4
+}
+; run
+
+function %fcvt_to_sint_sat(f32x4) -> i32x4 {
+block0(v0:f32x4):
+    v1 = fcvt_to_sint_sat.i32x4 v0
+    return v1
+}
+; run: %fcvt_to_sint_sat([0x0.0 -0x1.0 0x1.0 0x1.0p100]) == [0 -1 1 0x7FFFFFFF]
+; run: %fcvt_to_sint_sat([-0x8.1 0x0.0 0x0.0 -0x1.0p100]) == [-8 0 0 0x80000000]
+