gccrs: fix ice when setting up regions

num regions is based on the used arguments of regions which can be
less than the substutions requirements. So lets check for that and allow
anon regions to be created for them.

Fixes #3605

gcc/rust/ChangeLog:

	* typecheck/rust-tyty-subst.h: check for min range

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3605.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

Author: philberty

gcc/rust/typecheck/rust-tyty-subst.h

@@ -125,7 +125,7 @@ class RegionParamList
 				     std::vector<Region> subst)
   {
     RegionParamList list (num_regions);
-    for (size_t i = 0; i < subst.size (); i++)
+    for (size_t i = 0; i < MIN (num_regions, subst.size ()); i++)
       list.regions.at (i) = subst.at (i);
     for (size_t i = subst.size (); i < num_regions; i++)
       {

gcc/testsuite/rust/compile/issue-3605.rs

@@ -0,0 +1,5 @@
+enum Foo<'a> {}
+
+enum Bar<'a> {
+    in_band_def_explicit_impl(Foo<'a>),
+}