Building on GCC-based architectures after the upgrade to GCC8 requires
adding -Wno-unused-function -Wno-class-memaccess -Wno-catch-value to
CXXFLAGS and -Wno-format-overflow to CFLAGS.

PR: 234067
Submitted by: Piotr Kubaj
Approved by: portmgr (tier-2 blanket)