fix(libcxx)

needs system prefix to use libc++

projects/libcxx.llvm.org/package.yml

@@ -6,8 +6,6 @@ versions:
   github: llvm/llvm-project
   strip: /^llvmorg-/
 
-provides:
-
 build:
   dependencies:
     cmake.org: '>=3<3.29'
@@ -43,7 +41,7 @@ test:
   dependencies:
     llvm.org: '*'
   script:
-    - run: clang $ARGS $FIXTURE
+    - run: clang++ $ARGS $FIXTURE
       fixture:
         extname: cpp
         content: |
@@ -60,3 +58,4 @@ test:
       - -std=c++11
       - -stdlib=libc++
       - -lc++
+      - -isystem {{prefix}}/include/c++/v1