Avoid running one Rust test against older LLVM

LLVM 8.0 introduced some changes to let the Rust compiler emit DWARF
variant parts.  Before this change, the compiler would emit two types
with the same name, and unfortunately gdb happens to pick the wrong
one.  So, this patch disables the test when using an older version of
LLVM.

gdb/testsuite/ChangeLog
2020-09-15  Tom Tromey  <tromey@adacore.com>

	PR rust/26197:
	* lib/rust-support.exp (rust_llvm_version): New proc.
	* gdb.rust/simple.exp: Check rust_llvm_version.

1 files changed, 11 insertions, 2 deletions

diff --git a/gdb/testsuite/gdb.rust/simple.exp b/gdb/testsuite/gdb.rust/simple.exp
index b32eaf1..882c2e0 100644
--- a/gdb/testsuite/gdb.rust/simple.exp
+++ b/gdb/testsuite/gdb.rust/simple.exp
@@ -375,5 +375,14 @@ gdb_test "python print(e.type.fields()\[0\].artificial)" "True"
 gdb_test "python print(e.type.fields()\[1\].name)" "Two"
 
 gdb_test "python print(e.type.dynamic)" "False"
-gdb_test "python print(gdb.lookup_type('simple::MoreComplicated').dynamic)" \
-    "True"
+
+# Before LLVM 8, the rust compiler would emit two types named
+# "simple::MoreComplicated" -- the C-like "underlying" enum type and
+# the Rust enum.  lookup_type seems to get the former, which isn't
+# very useful.  With later versions of LLVM, this test works
+# correctly.
+set v [split [rust_llvm_version] .]
+if {[lindex $v 0] >= 8} {
+    gdb_test "python print(gdb.lookup_type('simple::MoreComplicated').dynamic)" \
+	"True"
+}