Rollup merge of #134999 - Berrysoft:dev/new-cygwin-target, r=chenyukang,workingjubilee

Add cygwin target.

This PR simply adds cygwin target together with msys2 target, based on ````@ookiineko```` 's (the account has been deleted) [work](https://github.com/ookiineko-cygport/rust) on cygwin target. My full work is here: https://github.com/rust-lang/rust/compare/master...Berrysoft:rust:dev/cygwin

I have succeeded in building a new rustc for cygwin target, and eventually distributed a new version of [fish-shell](https://github.com/Berrysoft/fish-shell/releases) (rewritten by Rust) for MSYS2.

I will open a new PR to fix std if this PR is accepted.

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

@@ -0,0 +1,46 @@
+use std::borrow::Cow;
+
+use crate::spec::{Cc, DebuginfoKind, LinkerFlavor, Lld, SplitDebuginfo, TargetOptions, cvs};
+
+pub(crate) fn opts() -> TargetOptions {
+    let mut pre_link_args = TargetOptions::link_args(
+        LinkerFlavor::Gnu(Cc::No, Lld::No),
+        &["--disable-dynamicbase", "--enable-auto-image-base"],
+    );
+    crate::spec::add_link_args(
+        &mut pre_link_args,
+        LinkerFlavor::Gnu(Cc::Yes, Lld::No),
+        &["-Wl,--disable-dynamicbase", "-Wl,--enable-auto-image-base"],
+    );
+    let cygwin_libs = &["-lcygwin", "-lgcc", "-lcygwin", "-luser32", "-lkernel32", "-lgcc_s"];
+    let mut late_link_args =
+        TargetOptions::link_args(LinkerFlavor::Gnu(Cc::No, Lld::No), cygwin_libs);
+    crate::spec::add_link_args(
+        &mut late_link_args,
+        LinkerFlavor::Gnu(Cc::Yes, Lld::No),
+        cygwin_libs,
+    );
+    TargetOptions {
+        os: "cygwin".into(),
+        vendor: "pc".into(),
+        // FIXME(#13846) this should be enabled for cygwin
+        function_sections: false,
+        linker: Some("gcc".into()),
+        dynamic_linking: true,
+        dll_prefix: "".into(),
+        dll_suffix: ".dll".into(),
+        exe_suffix: ".exe".into(),
+        families: cvs!["unix"],
+        is_like_windows: true,
+        allows_weak_linkage: false,
+        pre_link_args,
+        late_link_args,
+        abi_return_struct_as_int: true,
+        emit_debug_gdb_scripts: false,
+        requires_uwtable: true,
+        eh_frame_header: false,
+        debuginfo_kind: DebuginfoKind::Dwarf,
+        supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
+        ..Default::default()
+    }
+}

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

@@ -3,6 +3,7 @@ pub(crate) mod android;
 pub(crate) mod apple;
 pub(crate) mod avr_gnu;
 pub(crate) mod bpf;
+pub(crate) mod cygwin;
 pub(crate) mod dragonfly;
 pub(crate) mod freebsd;
 pub(crate) mod fuchsia;

compiler/rustc_target/src/spec/mod.rs

@@ -2013,6 +2013,7 @@ supported_targets! {
     ("riscv64imac-unknown-nuttx-elf", riscv64imac_unknown_nuttx_elf),
     ("riscv64gc-unknown-nuttx-elf", riscv64gc_unknown_nuttx_elf),
 
+    ("x86_64-pc-cygwin", x86_64_pc_cygwin),
 }
 
 /// Cow-Vec-Str: Cow<'static, [Cow<'static, str>]>
@@ -2994,8 +2995,8 @@ impl Target {
         );
         check_eq!(
             self.is_like_windows,
-            self.os == "windows" || self.os == "uefi",
-            "`is_like_windows` must be set if and only if `os` is `windows` or `uefi`"
+            self.os == "windows" || self.os == "uefi" || self.os == "cygwin",
+            "`is_like_windows` must be set if and only if `os` is `windows`, `uefi` or `cygwin`"
         );
         check_eq!(
             self.is_like_wasm,

compiler/rustc_target/src/spec/targets/x86_64_pc_cygwin.rs

@@ -0,0 +1,24 @@
+use crate::spec::{Cc, LinkerFlavor, Lld, Target, base};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::cygwin::opts();
+    base.cpu = "x86-64".into();
+    base.add_pre_link_args(LinkerFlavor::Gnu(Cc::No, Lld::No), &["-m", "i386pep"]);
+    base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
+    base.max_atomic_width = Some(64);
+    base.linker = Some("x86_64-pc-cygwin-gcc".into());
+    Target {
+        llvm_target: "x86_64-pc-cygwin".into(),
+        pointer_width: 64,
+        data_layout:
+            "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128".into(),
+        arch: "x86_64".into(),
+        options: base,
+        metadata: crate::spec::TargetMetadata {
+            description: Some("64-bit x86 Cygwin".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: None,
+        },
+    }
+}