Fix build: the symlink to libemosR64.a was not created
in ${STAGEDIR}, leading to fs_violations during poudriere test-builds.

--- libemos-sp/CMakeLists.txt.orig	2019-08-10 23:49:07 UTC
+++ libemos-sp/CMakeLists.txt
@@ -45,6 +45,6 @@ ecbuild_add_library(
 #               libemos.so ${CMAKE_INSTALL_PREFIX}/${INSTALL_LIB_DIR}/libemos.R32.D64.I32.so)" )
 #else()
   install(CODE "execute_process(COMMAND \"${CMAKE_COMMAND}\" -E create_symlink
-               libemos.a ${CMAKE_INSTALL_PREFIX}/${INSTALL_LIB_DIR}/libemos.R32.D64.I32.a)" )
+               libemos.a \$ENV{DESTDIR}/${CMAKE_INSTALL_PREFIX}/${INSTALL_LIB_DIR}/libemos.R32.D64.I32.a)" )
 #endif()