Toolchain: Build libLLVM as a dynamic library

This library is used by virtually all executables in the Clang
toolchain. By default, it is linked statically, which leads to huge
file sizes and us running out of artifact storage disk space on CI.

Toolchain/BuildClang.sh

@@ -259,6 +259,9 @@ pushd "$DIR/Build/clang/$ARCH"
             -DLLVM_ENABLE_PROJECTS="clang;lld" \
             -DLLVM_INCLUDE_BENCHMARKS=OFF \
             -DLLVM_INCLUDE_TESTS=OFF \
+            -DLLVM_LLVM_BUILD_LLVM_DYLIB=ON \
+            -DLLVM_LINK_LLVM_DYLIB=ON \
+            -DLLVM_INSTALL_UTILS=OFF \
             ${dev:+"-DLLVM_CCACHE_BUILD=ON"} || exit 1
 
         buildstep "llvm+clang/build" ninja -j "$MAKEJOBS" || exit 1