Don't overwrite default CMAKE_CXX_FLAGS in tests & samples

Change-Id: I4a2bb0bcc320fb0645e9fc5447775e6a878b960b

rocrtst/samples/CMakeLists.txt

@@ -179,8 +179,7 @@ add_definitions(-DLITTLEENDIAN_CPU=1)
 #
 # Linux Compiler options
 #
-set(CMAKE_CXX_FLAGS "-std=c++11 ")
-
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-math-errno")

rocrtst/suites/test_common/CMakeLists.txt

@@ -201,8 +201,7 @@ add_definitions(-DLITTLEENDIAN_CPU=1)
 #
 # Linux Compiler options
 #
-set(CMAKE_CXX_FLAGS "-std=c++11 ")
-
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 ")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-math-errno")