Use more targeted compile flags setup.

contrib/blake2/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 2.6)
 
 set(BLAKE_SRC blake2b-ref.c)
+add_library(blake2 STATIC "${BLAKE_SRC}")
 if ("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang" OR "${CMAKE_C_COMPILER_ID}" STREQUAL "GNU")
-	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O3")
+	set_target_properties(blake2 PROPERTIES COMPILER_FLAGS "-O3")
 endif ()
-add_library(blake2 STATIC "${BLAKE_SRC}")

contrib/libottery/CMakeLists.txt

@@ -3,7 +3,7 @@ SET(OTTERYSRC            chacha_merged.c
                          ottery_cpuinfo.c
                          ottery_entropy.c
                          ottery_global.c)
+ADD_LIBRARY(ottery STATIC ${OTTERYSRC})
 if ("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang" OR "${CMAKE_C_COMPILER_ID}" STREQUAL "GNU")
-	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O3")
-endif ()
-ADD_LIBRARY(ottery STATIC ${OTTERYSRC})  
+	set_target_properties(ottery PROPERTIES COMPILER_FLAGS "-O3")
+endif ()