- Fix build error on linux-x86-64bit-asan
  The problem was that a list of C flags are suppressed in the
  memcached code including -Wextra. Unfortunately this had an
  effect on a new flag -Wextra-semi which was incorrectly
  replaced with just -semi, something clang obviously complained
  about. Fixed the string replacement code such that -Wextra-semi
  remains untouched.