windows-gnullvm: Avoid linking to libunwind statically

Avoid linking against the static variant of libunwind, which is not
always available. Instead, prefer to use the unwind library from the
toolchain, which the linker will automatically include, depending
on what's available.

compiler/rustc_target/src/spec/base/windows_gnullvm.rs

@@ -6,10 +6,7 @@ pub fn opts() -> TargetOptions {
     // as a path since it's not added to linker search path by the default.
     // There were attempts to make it behave like libgcc (so one can just use -l<name>)
     // but LLVM maintainers rejected it: https://reviews.llvm.org/D51440
-    let pre_link_args = TargetOptions::link_args(
-        LinkerFlavor::Gnu(Cc::Yes, Lld::No),
-        &["-nolibc", "--unwindlib=none"],
-    );
+    let pre_link_args = TargetOptions::link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-nolibc"]);
     // Order of `late_link_args*` does not matter with LLD.
     let late_link_args = TargetOptions::link_args(
         LinkerFlavor::Gnu(Cc::Yes, Lld::No),

library/unwind/src/lib.rs

@@ -3,7 +3,6 @@
 #![feature(link_cfg)]
 #![feature(staged_api)]
 #![feature(c_unwind)]
-#![cfg_attr(bootstrap, feature(cfg_target_abi))]
 #![feature(strict_provenance)]
 #![cfg_attr(not(target_env = "msvc"), feature(libc))]
 #![allow(internal_features)]

library/unwind/src/libunwind.rs

@@ -102,12 +102,9 @@ pub type _Unwind_Exception_Cleanup_Fn =
 // rustc_codegen_ssa::src::back::symbol_export, rustc_middle::middle::exported_symbols
 // and RFC 2841
 #[cfg_attr(
-    any(
-        all(
-            feature = "llvm-libunwind",
-            any(target_os = "fuchsia", target_os = "linux", target_os = "xous")
-        ),
-        all(target_os = "windows", target_env = "gnu", target_abi = "llvm")
+    all(
+        feature = "llvm-libunwind",
+        any(target_os = "fuchsia", target_os = "linux", target_os = "xous")
     ),
     link(name = "unwind", kind = "static", modifiers = "-bundle")
 )]