[FYI] Clear rust_unions in rust_union_quirks

[Tom Tromey]

It turns out that a dwarf2_cu can remain allocated after psymtab
expansion is done, and so it makes sense to clear rust_unions when
done processing it.

Tested on x86-64 Fedora 27.

2018-05-14  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c (rust_union_quirks): Clear rust_unions.
---
 gdb/ChangeLog    | 4 ++++
 gdb/dwarf2read.c | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 67610d7144..d795b4a652 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2018-05-14  Tom Tromey  <tom@tromey.com>
+
+	* dwarf2read.c (rust_union_quirks): Clear rust_unions.
+
 2018-05-11  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* i387-tdep.c (i387_collect_xsave): Use FXSAVE_MXCSR_ADDR not
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 26ec5efc28..575d316cdd 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -10105,6 +10105,8 @@ rust_union_quirks (struct dwarf2_cu *cu)
   gdb_assert (cu->language == language_rust);
   for (struct type *type : cu->rust_unions)
     quirk_rust_enum (type, cu->per_cu->dwarf2_per_objfile->objfile);
+  /* We don't need this any more.  */
+  cu->rust_unions.clear ();
 }
 
 /* Return the symtab for PER_CU.  This works properly regardless of
-- 
2.14.3