Correct minimum system LLVM version in tests

Since commit 9452a8dfa3ba, the new debug info format is only generated
for LLVM 8 and newer versions. However, the tests still assume that LLVM
7 will use the new debug info format. Fix the tests (and a comment in
the code) to match the actual version check.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/librustc_codegen_llvm/debuginfo/metadata.rs b/src/librustc_codegen_llvm/debuginfo/metadata.rs
index ddcbf29da83..8efa025e3dd 100644
--- a/src/librustc_codegen_llvm/debuginfo/metadata.rs
+++ b/src/librustc_codegen_llvm/debuginfo/metadata.rs
@@ -1156,12 +1156,14 @@ fn prepare_union_metadata(
 // Enums
 //=-----------------------------------------------------------------------------
 
-// DWARF variant support is only available starting in LLVM 7.
+// DWARF variant support is only available starting in LLVM 8.
 // Although the earlier enum debug info output did not work properly
 // in all situations, it is better for the time being to continue to
 // sometimes emit the old style rather than emit something completely
-// useless when rust is compiled against LLVM 6 or older.  This
-// function decides which representation will be emitted.
+// useless when rust is compiled against LLVM 6 or older. LLVM 7
+// contains an early version of the DWARF variant support, and will
+// crash when handling the new debug info format. This function
+// decides which representation will be emitted.
 fn use_enum_fallback(cx: &CodegenCx<'_, '_>) -> bool {
     // On MSVC we have to use the fallback mode, because LLVM doesn't
     // lower variant parts to PDB.