compilers: add .stdcxx_libs to the compiler adaptor (#49873)

This property is used by a few recipes, including `cp2k` under
certain configurations

Signed-off-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

lib/spack/spack/compilers/adaptor.py

@@ -190,6 +190,10 @@ def f77(self):
         self._lang_exists_or_raise("f77", lang=Languages.FORTRAN)
         return self.compilers[Languages.FORTRAN].package.fortran
 
+    @property
+    def stdcxx_libs(self):
+        return self._maybe_return_attribute("stdcxx_libs", lang=Languages.CXX)
+
 
 class DeprecatedCompiler(lang.DeprecatedProperty):
     def __init__(self) -> None: