Add tests for -Zdwarf-version lto behavior

Author: wesleywiser

Diff for: tests/assembly/auxiliary/dwarf-mixed-versions-lto-aux.rs

@@ -0,0 +1,5 @@
+//@ compile-flags: -g --crate-type=rlib -Zdwarf-version=4
+
+pub fn check_is_even(number: &u64) -> bool {
+    number % 2 == 0
+}

Diff for: tests/assembly/dwarf-mixed-versions-lto.rs

@@ -0,0 +1,19 @@
+// This test ensures that if LTO occurs between crates with different DWARF versions, we
+// will choose the highest DWARF version for the final binary. This matches Clang's behavior.
+
+//@ only-linux
+//@ aux-build:dwarf-mixed-versions-lto-aux.rs
+//@ compile-flags: -C lto -g -Zdwarf-version=5
+//@ assembly-output: emit-asm
+//@ no-prefer-dynamic
+
+extern crate dwarf_mixed_versions_lto_aux;
+
+fn main() {
+    dwarf_mixed_versions_lto_aux::check_is_even(&0);
+}
+
+// CHECK: .section .debug_info
+// CHECK-NOT: {{\.(short|hword)}} 2
+// CHECK-NOT: {{\.(short|hword)}} 4
+// CHECK: {{\.(short|hword)}} 5

Diff for: tests/ui/lto/auxiliary/dwarf-mixed-versions-lto-aux.rs

@@ -0,0 +1,5 @@
+//@ compile-flags: -g --crate-type=rlib -Zdwarf-version=4
+
+pub fn say_hi() {
+    println!("hello there")
+}

Diff for: tests/ui/lto/dwarf-mixed-versions-lto.rs

@@ -0,0 +1,15 @@
+// This test verifies that we do not produce a warning when performing LTO on a
+// crate graph that contains a mix of different DWARF version settings. This
+// matches Clang's behavior.
+
+//@ ignore-msvc Platform must use DWARF
+//@ aux-build:dwarf-mixed-versions-lto-aux.rs
+//@ compile-flags: -C lto -g -Zdwarf-version=5
+//@ no-prefer-dynamic
+//@ build-pass
+
+extern crate dwarf_mixed_versions_lto_aux;
+
+fn main() {
+    dwarf_mixed_versions_lto_aux::say_hi();
+}

Diff for: tests/ui/lto/dwarf-mixed-versions-lto.stderr

@@ -0,0 +1,4 @@
+warning: linking module flags 'Dwarf Version': IDs have conflicting values ('i32 4' from  with 'i32 5' from dwarf_mixed_versions_lto.7f4a44b55cf2f174-cgu.0)
+
+warning: 1 warning emitted
+