ci: disable libc++ for clang for now

There is something wrong with the ubuntu env.

.ci/build-cs

@@ -11,7 +11,8 @@ current_triplet=`$CC -dumpmachine`
 
 if [ "$CC" = "clang" ]; then
     export CXX="clang++"
-    export CXXFLAGS="-stdlib=libc++"
+    # clang is busted in CI for some reason
+    #export CXXFLAGS="-stdlib=libc++"
 elif [ "$CC" = "gcc" ]; then
     export CXX="g++"
 else

.ci/install-env

@@ -30,7 +30,7 @@ mkdir -p host_tools
 
 echo ">> Updating package database..."
 
-[ -n "$is_linux" ] && sudo apt-get update && sudo apt-get install libc++-dev
+[ -n "$is_linux" ] && sudo apt-get update
 
 echo ">> Installing meson..."