Build: Add LLVM toolchain support for an521 only.

Support for other platforms will follow.

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: Id036ecd78bf8e8909af30f78b2bfe5262b78c6b9
diff --git a/cmake/install.cmake b/cmake/install.cmake
index d98bef1..b2e2d69 100644
--- a/cmake/install.cmake
+++ b/cmake/install.cmake
@@ -263,6 +263,7 @@
 install(FILES       ${PLATFORM_DIR}/ns/toolchain_ns_GNUARM.cmake
                     ${PLATFORM_DIR}/ns/toolchain_ns_ARMCLANG.cmake
                     ${PLATFORM_DIR}/ns/toolchain_ns_IARARM.cmake
+                    ${PLATFORM_DIR}/ns/toolchain_ns_LLVM.cmake
         DESTINATION ${INSTALL_CMAKE_DIR})
 
 install(FILES