Add clang-19 toolset

Author: igaztanaga

.github/workflows/ci.yml

@@ -309,6 +309,13 @@ jobs:
             container: ubuntu:24.04
             os: ubuntu-latest
             install: clang-18
+          # Linux, clang-19
+          - toolset: clang
+            compiler: clang++-19
+            cxxstd: "03,11,14,17,20,2b"
+            container: ubuntu:24.04
+            os: ubuntu-latest
+            install: clang-19
           # Linux, clang-15 libc++
           - toolset: clang
             compiler: clang++-15