Fix out-of-tree build by installing libllvmlibc (#2563)

LLVMExports.cmake from already installed packages references files
from the libllvmlibc package.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@d2b98fac642a0f6

Author: svenvh

llvm-spirv/.github/workflows/check-out-of-tree-build.yml

@@ -50,6 +50,7 @@ jobs:
           sudo apt-get -yq --no-install-suggests --no-install-recommends install \
             clang-${{ env.LLVM_VERSION }} \
             llvm-${{ env.LLVM_VERSION }}-dev \
+            libllvmlibc-${{ env.LLVM_VERSION }}-dev \
             libomp-${{ env.LLVM_VERSION }}-dev \
             llvm-${{ env.LLVM_VERSION }}-tools \
             mlir-${{ env.LLVM_VERSION }}-tools \