Rollup merge of rust-lang#71030 - petrochenkov:linkorder2, r=nagisa

rustc_target: Refactor target specifications related to Windows and UEFI

- LLD support is improved.
- Code is cleaned up.
- Target specs are organized in a more hierarchical way.
- Possible issues in UWP and UEFI platforms are identified (see FIXMEs).

The code is better read per-commit.

Author: Centril

src/librustc_codegen_ssa/back/link.rs

@@ -12,7 +12,7 @@ use rustc_session::search_paths::PathKind;
 /// need out of the shared crate context before we get rid of it.
 use rustc_session::{filesearch, Session};
 use rustc_span::symbol::Symbol;
-use rustc_target::spec::{LinkerFlavor, PanicStrategy, RelroLevel};
+use rustc_target::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelroLevel};
 
 use super::archive::ArchiveBuilder;
 use super::command::Command;
@@ -182,7 +182,9 @@ fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> Command {
     // To comply with the Windows App Certification Kit,
     // MSVC needs to link with the Store versions of the runtime libraries (vcruntime, msvcrt, etc).
     let t = &sess.target.target;
-    if flavor == LinkerFlavor::Msvc && t.target_vendor == "uwp" {
+    if (flavor == LinkerFlavor::Msvc || flavor == LinkerFlavor::Lld(LldFlavor::Link))
+        && t.target_vendor == "uwp"
+    {
         if let Some(ref tool) = msvc_tool {
             let original_path = tool.path();
             if let Some(ref root_lib_path) = original_path.ancestors().nth(4) {
@@ -1530,13 +1532,8 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
     cmd.debuginfo();
 
     // OBJECT-FILES-NO, AUDIT-ORDER
-    // We want to, by default, prevent the compiler from accidentally leaking in
-    // any system libraries, so we may explicitly ask linkers to not link to any
-    // libraries by default. Note that this does not happen for windows because
-    // windows pulls in some large number of libraries and I couldn't quite
-    // figure out which subset we wanted.
-    //
-    // This is all naturally configurable via the standard methods as well.
+    // We want to prevent the compiler from accidentally leaking in any system libraries,
+    // so by default we tell linkers not to link to any default libraries.
     if !sess.opts.cg.default_linker_libraries.unwrap_or(false)
         && sess.target.target.options.no_default_libraries
     {

src/librustc_codegen_ssa/back/linker.rs

@@ -631,15 +631,7 @@ impl<'a> Linker for MsvcLinker<'a> {
     }
 
     fn no_default_libraries(&mut self) {
-        // Currently we don't pass the /NODEFAULTLIB flag to the linker on MSVC
-        // as there's been trouble in the past of linking the C++ standard
-        // library required by LLVM. This likely needs to happen one day, but
-        // in general Windows is also a more controlled environment than
-        // Unix, so it's not necessarily as critical that this be implemented.
-        //
-        // Note that there are also some licensing worries about statically
-        // linking some libraries which require a specific agreement, so it may
-        // not ever be possible for us to pass this flag.
+        self.cmd.arg("/NODEFAULTLIB");
     }
 
     fn include_path(&mut self, path: &Path) {

src/librustc_target/spec/armebv7r_none_eabi.rs

@@ -1,7 +1,6 @@
 // Targets the Big endian Cortex-R4/R5 processor (ARMv7-R)
 
 use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, Target, TargetOptions, TargetResult};
-use std::default::Default;
 
 pub fn target() -> TargetResult {
     Ok(Target {

src/librustc_target/spec/armebv7r_none_eabihf.rs

@@ -1,7 +1,6 @@
 // Targets the Cortex-R4F/R5F processor (ARMv7-R)
 
 use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, Target, TargetOptions, TargetResult};
-use std::default::Default;
 
 pub fn target() -> TargetResult {
     Ok(Target {

src/librustc_target/spec/armv7r_none_eabi.rs

@@ -1,7 +1,6 @@
 // Targets the Little-endian Cortex-R4/R5 processor (ARMv7-R)
 
 use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, Target, TargetOptions, TargetResult};
-use std::default::Default;
 
 pub fn target() -> TargetResult {
     Ok(Target {

src/librustc_target/spec/armv7r_none_eabihf.rs

@@ -1,7 +1,6 @@
 // Targets the Little-endian Cortex-R4F/R5F processor (ARMv7-R)
 
 use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, Target, TargetOptions, TargetResult};
-use std::default::Default;
 
 pub fn target() -> TargetResult {
     Ok(Target {

src/librustc_target/spec/dragonfly_base.rs

@@ -1,5 +1,4 @@
 use crate::spec::{LinkArgs, LinkerFlavor, RelroLevel, TargetOptions};
-use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     let mut args = LinkArgs::new();

src/librustc_target/spec/freebsd_base.rs

@@ -1,5 +1,4 @@
 use crate::spec::{LinkArgs, LinkerFlavor, RelroLevel, TargetOptions};
-use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     let mut args = LinkArgs::new();

src/librustc_target/spec/fuchsia_base.rs

@@ -1,5 +1,4 @@
 use crate::spec::{LinkArgs, LinkerFlavor, LldFlavor, TargetOptions};
-use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     let mut pre_link_args = LinkArgs::new();

src/librustc_target/spec/haiku_base.rs

@@ -1,5 +1,4 @@
 use crate::spec::{RelroLevel, TargetOptions};
-use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {