Create x86_64-asan-linux-gnu target which enables ASAN by default

As suggested, in order to distribute sanitizer instrumented standard
libraries without introducing new rustc flags, this adds a new dedicated
target. With the target, we can distribute the instrumented standard
libraries through a separate rustup component.

Author: jakos-sec

compiler/rustc_target/src/spec/mod.rs

@@ -1800,6 +1800,8 @@ supported_targets! {
     ("x86_64-lynx-lynxos178", x86_64_lynx_lynxos178),
 
     ("x86_64-pc-cygwin", x86_64_pc_cygwin),
+
+    ("x86_64-asan-linux-gnu", x86_64_asan_linux_gnu),
 }
 
 /// Cow-Vec-Str: Cow<'static, [Cow<'static, str>]>

compiler/rustc_target/src/spec/targets/x86_64_asan_linux_gnu.rs

@@ -0,0 +1,31 @@
+use crate::spec::{
+    Arch, Cc, LinkerFlavor, Lld, SanitizerSet, StackProbeType, Target, TargetOptions, TargetMetadata, base,
+};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::linux_gnu::opts();
+    base.cpu = "x86-64".into();
+    base.plt_by_default = false;
+    base.max_atomic_width = Some(64);
+    base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
+    base.stack_probes = StackProbeType::Inline;
+    base.static_position_independent_executables = true;
+    base.supported_sanitizers = SanitizerSet::ADDRESS;
+    base.default_sanitizers = SanitizerSet::ADDRESS;
+    base.supports_xray = true;
+
+    Target {
+        llvm_target: "x86_64-unknown-linux-gnu".into(),
+        metadata: TargetMetadata {
+            description: Some("64-bit Linux (kernel 3.2+, glibc 2.17+)".into()),
+            tier: Some(1),
+            host_tools: Some(true),
+            std: Some(true),
+        },
+        pointer_width: 64,
+        data_layout:
+            "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128".into(),
+        arch: Arch::X86_64,
+        options: base,
+    }
+}

src/bootstrap/src/core/build_steps/llvm.rs

@@ -209,6 +209,7 @@ pub(crate) fn is_ci_llvm_available_for_target(
         ("i686-pc-windows-msvc", false),
         ("i686-unknown-linux-gnu", false),
         ("x86_64-unknown-linux-gnu", true),
+        ("x86_64-asan-linux-gnu", false),
         ("x86_64-apple-darwin", true),
         ("x86_64-pc-windows-gnu", true),
         ("x86_64-pc-windows-msvc", true),
@@ -1293,6 +1294,11 @@ fn supported_sanitizers(
             "x86_64",
             &["asan", "dfsan", "lsan", "msan", "safestack", "tsan", "rtsan"],
         ),
+        "x86_64-asan-linux-gnu" => common_libs(
+            "linux",
+            "x86_64",
+            &["asan"],
+        ),
         "x86_64-unknown-linux-musl" => {
             common_libs("linux", "x86_64", &["asan", "lsan", "msan", "tsan"])
         }

src/bootstrap/src/core/sanity.rs

@@ -42,6 +42,7 @@ const STAGE0_MISSING_TARGETS: &[&str] = &[
     // just a dummy comment so the list doesn't get onelined
     "riscv64gc-unknown-redox",
     "hexagon-unknown-qurt",
+    "x86_64-asan-linux-gnu",
 ];
 
 /// Minimum version threshold for libstdc++ required when using prebuilt LLVM