i386 target on BSDs doesn't include SSE2 by default

--- CMakeLists.txt.orig	2017-07-20 13:56:58 UTC
+++ CMakeLists.txt
@@ -204,6 +204,11 @@ if(ENABLE_AEC)
 			${AEC_SRC_DIR}/aec_core_sse2.c
 			${AEC_SRC_DIR}/aec_rdft_sse2.c
 		)
+		set_source_files_properties(
+			${AEC_SRC_DIR}/aec_core_sse2.c
+			${AEC_SRC_DIR}/aec_rdft_sse2.c
+			PROPERTIES COMPILE_FLAGS "-msse2"
+		)
 	endif()
 	include_directories(
 		${AEC_SRC_DIR}/include