cranelift: Add COFF TLS Support (#4546)

* cranelift: Implement COFF TLS Relocations

* cranelift: Emit SecRel relocations

* cranelift: Handle _tls_index symbol in backend

cranelift/filetests/filetests/isa/x64/tls_coff.clif

@@ -0,0 +1,20 @@
+test compile precise-output
+set tls_model=coff
+target x86_64
+
+
+function u0:0(i32) -> i64 {
+gv0 = symbol colocated tls u1:0
+
+block0(v0: i32):
+    v1 = global_value.i64 gv0
+    return v1
+}
+
+;   pushq   %rbp
+;   movq    %rsp, %rbp
+; block0:
+;   %rax = coff_tls_get_addr User { namespace: 1, index: 0 }
+;   movq    %rbp, %rsp
+;   popq    %rbp
+;   ret