cmake: fix build with GCC's UBSan

GNU GCC compiler has UndefinedBehaviour sanitizer support since
4.9.0 [1], but it was unsupported in tarantool's build. The patch
fixes a build by GNU GCC with enabled UBSan.

1. https://gcc.gnu.org/gcc-4.9/changes.html

NO_CHANGELOG=build
NO_DOC=build
NO_TEST=build

(cherry picked from commit 511e0f50e4b817d576ef4001611fba718ef1bdae)