add bots using lld (and examples with clang as a drive by) (#1221)

Fixes #1220 by adding 3 new bots:
* "With Clang and LLD on Ubuntu 20.04" https://buildkite.com/bazel/rules-rust-rustlang/builds/5799#5004ea2f-8c59-4fe4-9260-8798f7f13c11
* "Examples with Clang and LLD on Ubuntu 20.04" https://buildkite.com/bazel/rules-rust-rustlang/builds/5799#7e939a36-067e-4e0e-be54-07892bb164e1
* As a drive by I noticed there was no "Examples with Clang on Ubuntu 20.04", added it as well: https://buildkite.com/bazel/rules-rust-rustlang/builds/5799#beaddc14-4df3-446e-b02b-2836ae9f8d14.

Author: krasimirgg

.bazelci/presubmit.yml

@@ -121,8 +121,18 @@ tasks:
       - "--config=rustfmt"
       - "--config=clippy"
       - "--repo_env=CC=clang"
-      # TODO(hlopko): Make this work (some tests were failing)
-      # - "--linkopt=-fuse-ld=lld"
+    build_targets: *default_linux_targets
+    test_targets: *default_linux_targets
+  ubuntu2004_clang_lld:
+    name: With Clang and LLD
+    platform: ubuntu2004
+    shell_commands:
+      - "sudo apt -y update && sudo apt -y install lld"
+    build_flags:
+      - "--config=rustfmt"
+      - "--config=clippy"
+      - "--repo_env=CC=clang"
+      - "--linkopt=-fuse-ld=lld"
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
   ubuntu2004_rolling_clang:
@@ -132,8 +142,6 @@ tasks:
       - "--config=rustfmt"
       - "--config=clippy"
       - "--repo_env=CC=clang"
-      # TODO(hlopko): Make this work (some tests were failing)
-      # - "--linkopt=-fuse-ld=lld"
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     soft_fail: yes
@@ -191,6 +199,31 @@ tasks:
     test_targets:
       - "//..."
     build_flags: *aspects_flags
+  ubuntu2004_examples_clang:
+    name: Examples with Clang
+    platform: ubuntu2004
+    working_directory: examples
+    build_flags:
+      - "--repo_env=CC=clang"
+    build_targets:
+      - "//..."
+    test_targets:
+      - "//..."
+    build_flags: *aspects_flags
+  ubuntu2004_examples_clang_lld:
+    name: Examples with Clang and LLD
+    platform: ubuntu2004
+    shell_commands:
+      - "sudo apt -y update && sudo apt -y install lld"
+    working_directory: examples
+    build_flags:
+      - "--repo_env=CC=clang"
+      - "--linkopt=-fuse-ld=lld"
+    build_targets:
+      - "//..."
+    test_targets:
+      - "//..."
+    build_flags: *aspects_flags
   ubuntu2004_examples_rolling:
     name: "Examples with Rolling Bazel Version"
     platform: ubuntu2004