Add test default_function_param

Author: eopb

src/test/ui/const-generics/min_const_generics/default_function_param.rs

@@ -0,0 +1,6 @@
+#![feature(min_const_generics)]
+
+fn foo<const SIZE: usize = 5>() {}
+                      //~^ ERROR expected one of `!`, `(`, `+`, `,`, `::`, `<`, or `>`, found `=`
+
+fn main() {}

src/test/ui/const-generics/min_const_generics/default_function_param.stderr

@@ -0,0 +1,8 @@
+error: expected one of `!`, `(`, `+`, `,`, `::`, `<`, or `>`, found `=`
+  --> $DIR/default_function_param.rs:3:26
+   |
+LL | fn foo<const SIZE: usize = 5>() {}
+   |                          ^ expected one of 7 possible tokens
+
+error: aborting due to previous error
+