patch 8.2.0345: compiler warning when building without the float feature

Problem:    Compiler warning when building without the float feature.
Solution:   Add #ifdef. (John Marriott)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 363ac69..9e8e0fe 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -280,11 +280,13 @@
 {
     return &t_number;
 }
+#ifdef FEAT_FLOAT
     static type_T *
 ret_float(int argcount UNUSED, type_T **argtypes UNUSED)
 {
     return &t_float;
 }
+#endif
     static type_T *
 ret_string(int argcount UNUSED, type_T **argtypes UNUSED)
 {