Add i686-pc-windows-gnullvm triple

compiler/rustc_target/src/spec/i686_pc_windows_gnullvm.rs

@@ -0,0 +1,26 @@
+use crate::spec::{Cc, FramePointer, LinkerFlavor, Lld, Target};
+
+pub fn target() -> Target {
+    let mut base = super::windows_gnullvm_base::opts();
+    base.cpu = "pentium4".into();
+    base.max_atomic_width = Some(64);
+    base.frame_pointer = FramePointer::Always; // Required for backtraces
+    base.linker = Some("i686-w64-mingw32-clang".into());
+
+    // Mark all dynamic libraries and executables as compatible with the larger 4GiB address
+    // space available to x86 Windows binaries on x86_64.
+    base.add_pre_link_args(
+        LinkerFlavor::Gnu(Cc::No, Lld::No),
+        &["-m", "i386pe", "--large-address-aware"],
+    );
+
+    Target {
+        llvm_target: "i686-pc-windows-gnu".into(),
+        pointer_width: 32,
+        data_layout: "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
+            i64:64-f80:32-n8:16:32-a:0:32-S32"
+            .into(),
+        arch: "x86".into(),
+        options: base,
+    }
+}

compiler/rustc_target/src/spec/mod.rs

@@ -1420,6 +1420,7 @@ supported_targets! {
     ("x86_64-uwp-windows-gnu", x86_64_uwp_windows_gnu),
 
     ("aarch64-pc-windows-gnullvm", aarch64_pc_windows_gnullvm),
+    ("i686-pc-windows-gnullvm", i686_pc_windows_gnullvm),
     ("x86_64-pc-windows-gnullvm", x86_64_pc_windows_gnullvm),
 
     ("aarch64-pc-windows-msvc", aarch64_pc_windows_msvc),