Index: libcxx/trunk/CMakeLists.txt
===================================================================
--- libcxx/trunk/CMakeLists.txt
+++ libcxx/trunk/CMakeLists.txt
@@ -325,6 +325,11 @@
 
 # Required flags ==============================================================
 set(LIBCXX_STANDARD_VER c++11 CACHE INTERNAL "internal option to change build dialect")
+if (LIBCXX_HAS_MUSL_LIBC)
+  # musl's pthread implementations uses volatile types in their structs which is
+  # not a constexpr in C++11 but is in C++14, so we use C++14 with musl.
+  set(LIBCXX_STANDARD_VER c++14 CACHE INTERNAL "internal option to change build dialect")
+endif()
 add_compile_flags_if_supported(-std=${LIBCXX_STANDARD_VER})
 mangle_name("LIBCXX_SUPPORTS_STD_EQ_${LIBCXX_STANDARD_VER}_FLAG" SUPPORTS_DIALECT_NAME)
 if (NOT MSVC AND NOT ${SUPPORTS_DIALECT_NAME})