[libc++] Install PSTL when installing libc++ with parallel algorithms enabled

GitOrigin-RevId: 512c90389839a595ff592bf2f1345e0f1bc18530
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3e48d96..9c2db48 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -381,10 +381,14 @@
     if(LIBCXX_INSTALL_HEADERS)
       set(header_install_target install-cxx-headers)
     endif()
+    if (LIBCXX_ENABLE_PARALLEL_ALGORITHMS)
+      set(pstl_install_target install-pstl)
+    endif()
     add_custom_target(install-cxx
                       DEPENDS ${lib_install_target}
                               ${experimental_lib_install_target}
                               ${header_install_target}
+                              ${pstl_install_target}
                       COMMAND "${CMAKE_COMMAND}"
                       -DCMAKE_INSTALL_COMPONENT=cxx
                       -P "${LIBCXX_BINARY_DIR}/cmake_install.cmake")
@@ -392,6 +396,7 @@
                       DEPENDS ${lib_install_target}
                               ${experimental_lib_install_target}
                               ${header_install_target}
+                              ${pstl_install_target}
                       COMMAND "${CMAKE_COMMAND}"
                       -DCMAKE_INSTALL_COMPONENT=cxx
                       -DCMAKE_INSTALL_DO_STRIP=1