[build] Enable building riscv64 with clang.

Change-Id: Ie09d92a4e23484b7c6d2963bb0d327e443a68e46
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/338641
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

DEPS

@@ -517,6 +517,16 @@ Var("dart_root") + "/third_party/pkg/tar":
       "condition": "host_os == linux",
       "dep_type": "cipd",
   },
+  Var("dart_root") + "/buildtools/sysroot/focal": {
+      "packages": [
+          {
+              "package": "fuchsia/third_party/sysroot/focal",
+              "version": "git_revision:fa7a5a9710540f30ff98ae48b62f2cdf72ed2acd",
+          },
+      ],
+      "condition": "host_os == linux",
+      "dep_type": "cipd",
+  },
 
   # Keep consistent with pkg/test_runner/lib/src/options.dart.
   Var("dart_root") + "/buildtools/linux-x64/clang": {

build/config/compiler/BUILD.gn

@@ -422,8 +422,20 @@ config("compiler") {
       toolchain_stamp_file =
           "//buildtools/mac-x64/clang/.versions/clang.cipd_version"
     }
-    cipd_version = read_file(toolchain_stamp_file, "json")
+    toolchain_cipd_version = read_file(toolchain_stamp_file, "json")
-    defines = [ "TOOLCHAIN_VERSION=${cipd_version.instance_id}" ]
+    defines = [ "TOOLCHAIN_VERSION=${toolchain_cipd_version.instance_id}" ]
+
+    if (is_linux) {
+      if (current_cpu == "riscv64") {
+        sysroot_stamp_file =
+            "//buildtools/sysroot/focal/.versions/sysroot.cipd_version"
+      } else {
+        sysroot_stamp_file =
+            "//buildtools/sysroot/linux/.versions/sysroot.cipd_version"
+      }
+      sysroot_cipd_version = read_file(sysroot_stamp_file, "json")
+      defines += [ "SYSROOT_VERSION=${sysroot_cipd_version.instance_id}" ]
+    }
   }
 
   # Assign any flags set for the C compiler to asmflags so that they are sent

build/config/sysroot.gni

@@ -37,7 +37,12 @@ if (is_linux) {
       assert(false)
     }
   } else if (dart_sysroot == "debian") {
-    target_sysroot = rebase_path("//buildtools/sysroot/linux", root_build_dir)
+    if (current_cpu == "riscv64") {
+      target_sysroot = rebase_path("//buildtools/sysroot/focal", root_build_dir)
+    } else {
+      # Updating to focal would increase the required libc from 2.17 to 2.28.
+      target_sysroot = rebase_path("//buildtools/sysroot/linux", root_build_dir)
+    }
   } else if (dart_sysroot != "") {
     print("There is no $dart_sysroot sysroot support")
     assert(false)

pkg/test_runner/lib/src/compiler_configuration.dart

@@ -933,16 +933,13 @@ class PrecompilerCompilerConfiguration extends CompilerConfiguration
     var exec = _configuration.genSnapshotPath;
     if (exec == null) {
       var gcc32 = "<does-not-exist>";
-      var gcc64 = "<does-not-exist>";
       var clang32 = "<does-not-exist>";
       var clang64 = "<does-not-exist>";
       if (Architecture.host == Architecture.x64) {
         gcc32 = "x86";
-        gcc64 = "x64";
         clang32 = "clang_x86";
         clang64 = "clang_x64";
       } else if (Architecture.host == Architecture.arm64) {
-        gcc64 = "arm64";
         clang64 = "clang_arm64";
       }
       if (_isAndroid) {
@@ -966,7 +963,7 @@ class PrecompilerCompilerConfiguration extends CompilerConfiguration
       } else if (_isRiscv32 && _configuration.useQemu) {
         exec = "$buildDir/$gcc32/gen_snapshot";
       } else if (_isRiscv64 && _configuration.useQemu) {
-        exec = "$buildDir/$gcc64/gen_snapshot";
+        exec = "$buildDir/$clang64/gen_snapshot";
       } else {
         exec = "$buildDir/gen_snapshot";
       }

tools/bots/test_matrix.json

@@ -877,8 +877,6 @@
           "name": "build dart",
           "script": "tools/build.py",
           "arguments": [
-            "--no-clang",
-            "--no-goma",
             "--use-qemu",
             "dart_precompiled_runtime",
             "runtime"