Revert "[build] Update to Focal sysroot."

This reverts commit ad9a13a1c1.

Reason for revert: breaks Debian arm32 package

Original change's description:
> [build] Update to Focal sysroot.
>
> Our minimum supported version is Jammy, which Fuchsia doesn't have a CIPD package for, but at least we no longer need to use a different sysroot for different architectures.
>
> Change-Id: I90f37797c2f2f79886df85d6b7ed9903270e8c2a
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/433561
> Reviewed-by: Alexander Aprelev <aam@google.com>
> Commit-Queue: Ryan Macnak <rmacnak@google.com>

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I532c6052ba9bfe271f34bc18f6120eb80df98d6f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/433922
Auto-Submit: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>

DEPS

@@ -386,6 +386,16 @@ deps = {
   Var("dart_root") + "/third_party/pkg/web":
       Var("dart_git") + "web.git" + "@" + Var("web_rev"),
 
+  Var("dart_root") + "/buildtools/sysroot/linux": {
+      "packages": [
+          {
+              "package": "fuchsia/third_party/sysroot/linux",
+              "version": "git_revision:fa7a5a9710540f30ff98ae48b62f2cdf72ed2acd",
+          },
+      ],
+      "condition": "host_os == linux",
+      "dep_type": "cipd",
+  },
   Var("dart_root") + "/buildtools/sysroot/focal": {
       "packages": [
           {

build/config/compiler/BUILD.gn

@@ -414,8 +414,13 @@ config("compiler") {
     defines = [ "TOOLCHAIN_VERSION=${toolchain_cipd_version.instance_id}" ]
 
     if (is_linux) {
-      sysroot_stamp_file =
-          "//buildtools/sysroot/focal/.versions/sysroot.cipd_version"
+      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}" ]
     }

build/config/sysroot.gni

@@ -37,7 +37,12 @@ if (is_linux) {
       assert(false)
     }
   } else if (dart_sysroot == "debian") {
-    target_sysroot = rebase_path("//buildtools/sysroot/focal", 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)