Add cxx_std_11 feature to PCU (#533)

std::unique_ptr was introduced in C++11 and required for the new public PCU interface.

Author: bobpaw

pcu/CMakeLists.txt

@@ -41,6 +41,7 @@ set(HEADERS
 
 # Add the pcu library
 add_library(pcu ${SOURCES})
+target_compile_features(pcu PUBLIC cxx_std_11)
 # this compiler definition is needed to silence warnings caused by the openmpi CXX
 # bindings that are depreciated. This is needed on gcc 8 forward.
 # see: https://github.com/open-mpi/ompi/issues/5157