Prevent overriding of user-define CFLAGS, including -march flag.

    The flag -msse4.1 is required otherwise compile will not be able to inline sse4.1 code.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -52,6 +52,8 @@ option (BUILD_CMRTLIB "Build and Install cmrtlib together with media driver" ON)
 
 option (ENABLE_PRODUCTION_KMD "Enable Production KMD header files" OFF)
 
+option (OVERRIDE_COMPILER_FLAGS "Override user compiler FLAGS and use lib defaults" ON)
+
 include(GNUInstallDirs)
 
 if (BUILD_CMRTLIB)

--- a/cmrtlib/linux/CMakeLists.txt
+++ b/cmrtlib/linux/CMakeLists.txt
@@ -33,15 +33,19 @@ endif()
 
 # Set up compile options that will be used for the Linux build
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CPP_STANDARD_OPTION} -fPIC -fpermissive -fstack-protector-all -Werror")
+if (OVERRIDE_COMPILER_FLAGS)
 if(CMAKE_SIZEOF_VOID_P EQUAL 8)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse4.1")
 endif()
+endif()
 set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fno-strict-aliasing -D_FORTIFY_SOURCE=2")
 set(CMAKE_CXX_FLAGS_DEBUG   "${CMAKE_CXX_FLAGS_DEBUG} -D_DEBUG -D__DEBUG -O0")
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${CPP_STANDARD_OPTION} -fPIC -fpermissive -fstack-protector-all -Werror")
+if (OVERRIDE_COMPILER_FLAGS)
 if(CMAKE_SIZEOF_VOID_P EQUAL 8)
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -msse4.1")
 endif()
+endif()
 set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -fno-strict-aliasing -D_FORTIFY_SOURCE=2")
 set(CMAKE_C_FLAGS_DEBUG   "${CMAKE_C_FLAGS_DEBUG} -D_DEBUG -D__DEBUG -O0")
 

--- a/media_driver/cmake/linux/media_compile_flags_linux.cmake
+++ b/media_driver/cmake/linux/media_compile_flags_linux.cmake
@@ -36,7 +36,10 @@ set(MEDIA_COMPILER_FLAGS_COMMON
     -Werror=format-security
     -Werror=non-virtual-dtor
     -Werror=return-type
+)
 
+if (OVERRIDE_COMPILER_FLAGS)
+    list (APPEND MEDIA_COMPILER_FLAGS_COMMON
     # General optimization options
     -march=${UFO_MARCH}
     -mpopcnt
@@ -44,23 +47,33 @@ set(MEDIA_COMPILER_FLAGS_COMMON
     -msse2
     -msse3
     -mssse3
-    -msse4.1
     -msse4.2
     -msse4
+)
+endif(OVERRIDE_COMPILER_FLAGS)
+
+list (APPEND MEDIA_COMPILER_FLAGS_COMMON
+    -msse4.1	# SSE4.1 support is required to build the library
     -mfpmath=sse
     -finline-functions
     -funswitch-loops
     -fno-short-enums
     -Wa,--noexecstack
     -fno-strict-aliasing
+)
 
+if (OVERRIDE_COMPILER_FLAGS)
+    list (APPEND MEDIA_COMPILER_FLAGS_COMMON
     # Common defines
     -DUSE_MMX
     -DUSE_SSE
     -DUSE_SSE2
     -DUSE_SSE3
     -DUSE_SSSE3
+)
+endif(OVERRIDE_COMPILER_FLAGS)
 
+list (APPEND MEDIA_COMPILER_FLAGS_COMMON
     # Other common flags
     -fmessage-length=0
     -fvisibility=hidden
@@ -68,16 +81,26 @@ set(MEDIA_COMPILER_FLAGS_COMMON
     -fdata-sections
     -ffunction-sections
     -Wl,--gc-sections
+)
 
+if (OVERRIDE_COMPILER_FLAGS)
+    list (APPEND MEDIA_COMPILER_FLAGS_COMMON
     # -m32 or -m64
     -m${ARCH}
+)
+endif(OVERRIDE_COMPILER_FLAGS)
 
+list (APPEND MEDIA_COMPILER_FLAGS_COMMON
     # Global defines
     -DLINUX=1
     -DLINUX
     -DNO_RTTI
     -DNO_EXCEPTION_HANDLING
     -DINTEL_NOT_PUBLIC
+)
+
+if (OVERRIDE_COMPILER_FLAGS)
+    list (APPEND MEDIA_COMPILER_FLAGS_COMMON
     -g
 )
 
@@ -90,6 +113,7 @@ if(${UFO_MARCH} STREQUAL "slm")
         -mtune=atom
     )
 endif()
+endif(OVERRIDE_COMPILER_FLAGS)
 
 if(${ARCH} STREQUAL "64")
     set(MEDIA_COMPILER_FLAGS_COMMON
@@ -206,9 +230,11 @@ include(${MEDIA_EXT_CMAKE}/ext/linux/media_compile_flags_linux_ext.cmake OPTIONA
 if(${PLATFORM} STREQUAL "linux")
     #set predefined compiler flags set
     add_compile_options("${MEDIA_COMPILER_FLAGS_COMMON}")
+if (OVERRIDE_COMPILER_FLAGS)
     add_compile_options("$<$<CONFIG:Debug>:${MEDIA_COMPILER_FLAGS_DEBUG}>")
     add_compile_options("$<$<CONFIG:Release>:${MEDIA_COMPILER_FLAGS_RELEASE}>")
     add_compile_options("$<$<CONFIG:ReleaseInternal>:${MEDIA_COMPILER_FLAGS_RELEASEINTERNAL}>")
+endif(OVERRIDE_COMPILER_FLAGS)
 
     foreach (flag ${MEDIA_COMPILER_CXX_FLAGS_COMMON})
         SET (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}")