Unify gcc and clang cmake flags to test with UBsan

Previously, not all flags were supported by the gcc version that was used
(pre-4.9). Now, since the minimum version gcc version tested is 5.4, 
the flags can be unified.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 16d7197..81fa6cb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -137,8 +137,8 @@
     set(CMAKE_C_FLAGS_RELEASE     "-O2")
     set(CMAKE_C_FLAGS_DEBUG       "-O0 -g3")
     set(CMAKE_C_FLAGS_COVERAGE    "-O0 -g3 --coverage")
-    set(CMAKE_C_FLAGS_ASAN        "-Werror -fsanitize=address -fno-common -O3")
-    set(CMAKE_C_FLAGS_ASANDBG     "-Werror -fsanitize=address -fno-common -O1 -g3 -fno-omit-frame-pointer -fno-optimize-sibling-calls ")
+    set(CMAKE_C_FLAGS_ASAN        "-Werror -fsanitize=address -fno-common -fsanitize=undefined -fno-sanitize-recover=all -O3")
+    set(CMAKE_C_FLAGS_ASANDBG     "-Werror -fsanitize=address -fno-common -fsanitize=undefined -fno-sanitize-recover=all -O1 -g3 -fno-omit-frame-pointer -fno-optimize-sibling-calls")
     set(CMAKE_C_FLAGS_CHECK       "-Werror -Os")
     set(CMAKE_C_FLAGS_CHECKFULL   "${CMAKE_C_FLAGS_CHECK} -Wcast-qual")
 endif(CMAKE_COMPILER_IS_GNU)
@@ -149,7 +149,7 @@
     set(CMAKE_C_FLAGS_DEBUG       "-O0 -g3")
     set(CMAKE_C_FLAGS_COVERAGE    "-O0 -g3 --coverage")
     set(CMAKE_C_FLAGS_ASAN        "-Werror -fsanitize=address -fno-common -fsanitize=undefined -fno-sanitize-recover=all -O3")
-    set(CMAKE_C_FLAGS_ASANDBG     "-Werror -fsanitize=address -fno-common -fsanitize=undefined -fno-sanitize-recover=all -O1 -g3 -fno-omit-frame-pointer -fno-optimize-sibling-calls ")
+    set(CMAKE_C_FLAGS_ASANDBG     "-Werror -fsanitize=address -fno-common -fsanitize=undefined -fno-sanitize-recover=all -O1 -g3 -fno-omit-frame-pointer -fno-optimize-sibling-calls")
     set(CMAKE_C_FLAGS_MEMSAN      "-Werror -fsanitize=memory -O3")
     set(CMAKE_C_FLAGS_MEMSANDBG   "-Werror -fsanitize=memory -O1 -g3 -fno-omit-frame-pointer -fno-optimize-sibling-calls -fsanitize-memory-track-origins=2")
     set(CMAKE_C_FLAGS_CHECK       "-Werror -Os")