[libc++] Switch to the new docker image in the CI (#185843)

This also simplifies the workflow file a bit and removes a redundant
`generic-cxx26` configuration in stage 3.

.github/workflows/libcxx-build-and-test.yaml

@@ -36,7 +36,7 @@ concurrency:
 jobs:
   stage1:
     if: github.repository_owner == 'llvm'
-    runs-on: llvm-premerge-libcxx-runners
+    runs-on: llvm-premerge-libcxx-next-runners
     continue-on-error: false
     strategy:
       fail-fast: false
@@ -73,7 +73,7 @@ jobs:
             **/crash_diagnostics/*
   stage2:
     if: github.repository_owner == 'llvm'
-    runs-on: llvm-premerge-libcxx-runners
+    runs-on: llvm-premerge-libcxx-next-runners
     needs: [ stage1 ]
     continue-on-error: false
     strategy:
@@ -118,6 +118,7 @@ jobs:
             **/crash_diagnostics/*
   stage3:
     if: github.repository_owner == 'llvm'
+    runs-on: llvm-premerge-libcxx-next-runners
     needs: [ stage2 ]
     continue-on-error: false
     strategy:
@@ -146,24 +147,13 @@ jobs:
           'generic-no-rtti',
           'generic-optimized-speed',
           'generic-static',
+          'generic-asan',
+          'generic-asan-in-tests-only',
+          'generic-tsan',
+          'generic-ubsan',
+          'generic-msan',
           'bootstrapping-build'
         ]
-        machine: [ 'llvm-premerge-libcxx-runners' ]
-        include:
-        - config: 'generic-cxx26'
-          machine: llvm-premerge-libcxx-runners
-        - config: 'generic-asan'
-          machine: llvm-premerge-libcxx-runners
-        - config: 'generic-asan-in-tests-only'
-          machine: llvm-premerge-libcxx-runners
-        - config: 'generic-tsan'
-          machine: llvm-premerge-libcxx-runners
-        - config: 'generic-ubsan'
-          machine: llvm-premerge-libcxx-runners
-        # Use a larger machine for MSAN to avoid timeout and memory allocation issues.
-        - config: 'generic-msan'
-          machine: llvm-premerge-libcxx-runners
-    runs-on: ${{ matrix.machine }}
     steps:
       - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
       - name: ${{ matrix.config }}

libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp

@@ -732,7 +732,7 @@ void mi_mode_test() {
   one_two_three_umap.insert({2, "two"});
   one_two_three_umap.insert({1, "one"});
   CompareListChildrenToChars(
-      one_two_three_umap, R"([{"key": 3, "value": "three"}, {"key": 2, "value": "two"}, {"key": 1, "value": "one"}])");
+      one_two_three_umap, R"([{"key": 1, "value": "one"}, {"key": 2, "value": "two"}, {"key": 3, "value": "three"}])");
 
   std::deque<int> one_two_three_deque{1, 2, 3};
   CompareListChildrenToChars(one_two_three_deque, "[1, 2, 3]");