Make `rust.download-ci-llvm="if-available"` work for tier 2 platforms.

src/bootstrap/bootstrap.py

@@ -492,10 +492,11 @@ class RustBuild(object):
 
     def downloading_llvm(self):
         opt = self.get_toml('download-ci-llvm', 'llvm')
-        # This is currently all tier 1 targets (since others may not have CI
-        # artifacts)
+        # This is currently all tier 1 targets and tier 2 targets with host tools
+        # (since others may not have CI artifacts)
         # https://doc.rust-lang.org/rustc/platform-support.html#tier-1
         supported_platforms = [
+            # tier 1
             "aarch64-unknown-linux-gnu",
             "i686-pc-windows-gnu",
             "i686-pc-windows-msvc",
@@ -504,6 +505,26 @@ class RustBuild(object):
             "x86_64-apple-darwin",
             "x86_64-pc-windows-gnu",
             "x86_64-pc-windows-msvc",
+            # tier 2 with host tools
+            "aarch64-apple-darwin",
+            "aarch64-pc-windows-msvc",
+            "aarch64-unknown-linux-musl",
+            "arm-unknown-linux-gnueabi",
+            "arm-unknown-linux-gnueabihf",
+            "armv7-unknown-linux-gnueabihf",
+            "mips-unknown-linux-gnu",
+            "mips64-unknown-linux-gnuabi64",
+            "mips64el-unknown-linux-gnuabi64",
+            "mipsel-unknown-linux-gnu",
+            "powerpc-unknown-linux-gnu",
+            "powerpc64-unknown-linux-gnu",
+            "powerpc64le-unknown-linux-gnu",
+            "riscv64gc-unknown-linux-gnu",
+            "s390x-unknown-linux-gnu",
+            "x86_64-unknown-freebsd",
+            "x86_64-unknown-illumos",
+            "x86_64-unknown-linux-musl",
+            "x86_64-unknown-netbsd",
         ]
         return opt == "true" \
             or (opt == "if-available" and self.build in supported_platforms)

src/bootstrap/config.rs

@@ -765,10 +765,12 @@ pub fn parse(args: &[String]) -> Config {
             config.llvm_from_ci = match llvm.download_ci_llvm {
                 Some(StringOrBool::String(s)) => {
                     assert!(s == "if-available", "unknown option `{}` for download-ci-llvm", s);
-                    // This is currently all tier 1 targets (since others may not have CI artifacts)
+                    // This is currently all tier 1 targets and tier 2 targets with host tools
+                    // (since others may not have CI artifacts)
                     // https://doc.rust-lang.org/rustc/platform-support.html#tier-1
                     // FIXME: this is duplicated in bootstrap.py
                     let supported_platforms = [
+                        // tier 1
                         "aarch64-unknown-linux-gnu",
                         "i686-pc-windows-gnu",
                         "i686-pc-windows-msvc",
@@ -777,6 +779,26 @@ pub fn parse(args: &[String]) -> Config {
                         "x86_64-apple-darwin",
                         "x86_64-pc-windows-gnu",
                         "x86_64-pc-windows-msvc",
+                        // tier 2 with host tools
+                        "aarch64-apple-darwin",
+                        "aarch64-pc-windows-msvc",
+                        "aarch64-unknown-linux-musl",
+                        "arm-unknown-linux-gnueabi",
+                        "arm-unknown-linux-gnueabihf",
+                        "armv7-unknown-linux-gnueabihf",
+                        "mips-unknown-linux-gnu",
+                        "mips64-unknown-linux-gnuabi64",
+                        "mips64el-unknown-linux-gnuabi64",
+                        "mipsel-unknown-linux-gnu",
+                        "powerpc-unknown-linux-gnu",
+                        "powerpc64-unknown-linux-gnu",
+                        "powerpc64le-unknown-linux-gnu",
+                        "riscv64gc-unknown-linux-gnu",
+                        "s390x-unknown-linux-gnu",
+                        "x86_64-unknown-freebsd",
+                        "x86_64-unknown-illumos",
+                        "x86_64-unknown-linux-musl",
+                        "x86_64-unknown-netbsd",
                     ];
                     supported_platforms.contains(&&*config.build.triple)
                 }