posix: fpu: Fix compiler error when enabling fpu on posix boards

Enabling CONFIG_FPU and CONFIG_FPU_SHARING requires the
definition of `arch_float_disable` and `arch_float_enable`.

Signed-off-by: Matthias Alleman <matthias.alleman@basalte.be>
(cherry picked from commit e7c353bf14)

arch/posix/core/thread.c

@@ -61,6 +61,25 @@ void posix_arch_thread_entry(void *pa_thread_status)
 	z_thread_entry(ptr->entry_point, ptr->arg1, ptr->arg2, ptr->arg3);
 }
 
+#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
+int arch_float_disable(struct k_thread *thread)
+{
+	ARG_UNUSED(thread);
+
+	/* Posix always has FPU enabled so cannot be disabled */
+	return -ENOTSUP;
+}
+
+int arch_float_enable(struct k_thread *thread, unsigned int options)
+{
+	ARG_UNUSED(thread);
+	ARG_UNUSED(options);
+
+	/* Posix always has FPU enabled so nothing to do here */
+	return 0;
+}
+#endif /* CONFIG_FPU && CONFIG_FPU_SHARING */
+
 #if defined(CONFIG_ARCH_HAS_THREAD_ABORT)
 void z_impl_k_thread_abort(k_tid_t thread)
 {