The upcoming MAME 0.215 release will be the last version that can be compiled with GCC 5 or GCC 6. Going forward, the minimum supported compiler will be GCC 7.2 or clang 5. The Windows development tools have included GCC 7.4 for some time already, so you won’t need to update unless you haven’t in a very long time.
MAME 0.217 will be the last release with pre-built 32-bit Windows binaries supplied. Starting in 2020, you’ll need to compile MAME yourself if you want a 32-bit version. We’ll still support building for 32-bit architectures, but optimisation for 32-bit x86 will not be a priority.