<html>
    <head>
      <base href="http://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - argument unused during compilation: '-stdlib=libc++'"
   href="http://llvm.org/bugs/show_bug.cgi?id=20395">20395</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>argument unused during compilation: '-stdlib=libc++'
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libc++abi
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>All Bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>oroppas@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu, mclow.lists@gmail.com
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>libcxxabi/src/*.cpp are compiled with '-nostdinc++' and building with 
LLVM_ENABLE_LIBCXX:BOOL=ON issues the warning like

  [48/1203] Building CXX object
  projects/libcxxabi/src/CMakeFiles/cxxabi.dir/cxa_demangle.cpp.o
  clang-3.5: warning: argument unused during compilation: '-stdlib=libc++'

for all *.cpp in libcxxabi.

Simply removing '-stdlib=libc++' for compilation of libcxxabi/src/*.cpp should
fix the problem.

Index: llvm/projects/libcxxabi/CMakeLists.txt
===================================================================
--- llvm/projects/libcxxabi/CMakeLists.txt    (revision 213616)
+++ llvm/projects/libcxxabi/CMakeLists.txt    (working copy)
@@ -124,7 +124,7 @@
         ${LLVM_INCLUDE_DIR}/c++/v1
   )

-set(LIBCXXABI_LIBCXX_INCLUDES "${LIBCXXABI_LIBCXX_INCLUDES}" CACHE STRING
+set(LIBCXXABI_LIBCXX_INCLUDES "${LIBCXXABI_LIBCXX_INCLUDES}" CACHE PATH
     "Specify path to libc++ includes." FORCE)


#===============================================================================
@@ -154,6 +154,7 @@

 if (LIBCXXABI_HAS_NOSTDINCXX_FLAG)
   list(APPEND LIBCXXABI_CXX_REQUIRED_FLAGS -nostdinc++)
+  string(REPLACE "-stdlib=libc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()

 append_if(LIBCXXABI_CXX_REQUIRED_FLAGS LIBCXXABI_HAS_WERROR_FLAG
-Werror=return-type)</pre>
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