linux: use find_library to find the sodium library

Just so that we fail at configure time if it's not present.

bin/GCStress/CMakeLists.txt

@@ -13,7 +13,10 @@ target_include_directories (GCStress
   $<BUILD_INTERFACE:${ROOT_SOURCE_DIR}/lib/Common/Memory>  
   )
 
-set(CMAKE_EXE_LINKER_FLAGS "-lsodium")
+find_library(SODIUM_PATH sodium)
+if (NOT SODIUM_PATH)
+  message(FATAL_ERROR "Sodium library is needed to build GCStress")
+endif (NOT SODIUM_PATH)
 
 target_link_libraries (GCStress
   PRIVATE Chakra.Common.Memory
@@ -22,5 +25,6 @@ target_link_libraries (GCStress
   PRIVATE Chakra.Common.DataStructures
   PRIVATE Chakra.Common.Exceptions
   PRIVATE Chakra.Pal
+  ${SODIUM_PATH}
   )