cranelift: Merge all run tests into runtests dir

With this change we now reuse tests across multiple arches.

Duplicate tests were merged into the same file where possible.
Some legacy x86 tests were left in separate files due to incompatibilities with the rest of the test suite.

cranelift/filetests/filetests/runtests/extend.clif

@@ -0,0 +1,30 @@
+test run
+target aarch64
+target arm
+target s390x
+; target x86_64 machinst TODO: Not yet implemented on x86_64
+target i686 legacy
+
+function %uextend() -> b1 {
+block0:
+    v0 = iconst.i32 0xffff_ee00
+    v1 = uextend.i64 v0
+    v2, v3 = isplit v1
+    v4 = icmp_imm eq v2, 0xffff_ee00
+    v5 = icmp_imm eq v3, 0
+    v6 = band v4, v5
+    return v6
+}
+; run
+
+function %sextend() -> b1 {
+block0:
+    v0 = iconst.i32 0xffff_ee00
+    v1 = sextend.i64 v0
+    v2, v3 = isplit v1
+    v4 = icmp_imm eq v2, 0xffff_ee00
+    v5 = icmp_imm eq v3, 0xffff_ffff
+    v6 = band v4, v5
+    return v6
+}
+; run