[CI] Include -DLLVM_BYILD_LLVM_DYLIB on Darwin

This extra CMake flag makse sure that libLLVM.dylib is built, which is
required when using `clang` from HomeBrew (which is built with LTO
enabled).

.github/workflows/x86-darwin-llvm-from-sources.yml

@@ -32,6 +32,7 @@ jobs:
             -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
             -DLLVM_TARGETS_TO_BUILD="X86" \
             -DLLVM_OPTIMIZED_TABLEGEN=ON \
+            -DLLVM_BUILD_LLVM_DYLIB=ON \
             -DDEFAULT_SYSROOT="$(xcrun --show-sdk-path)" \
             ../llvm
           ninja

tools/CMakeLists.txt

@@ -34,6 +34,9 @@ set(ct-code-style-checker_SOURCES
 #    triggered for static libs)
 #  * `libclang-cpp`/`libLLVM` include all Clang/LLVM libraries (i.e. all the
 #    libraries listed below _and more_)
+#
+# TODO: Once LLVM 16 is released, replace `try_compile` with a test for
+# LLVM_ENABLE_LTO, see https://reviews.llvm.org/D134936.
 set(libs "clangTooling")
 
 try_compile(testMinimalCompilation "${CMAKE_BINARY_DIR}/temp" SOURCES