x86-64: Only define used SSE/AVX/AVX512 run-time resolvers

When glibc is built with x86-64 ISA level v3, SSE run-time resolvers
aren't used.  For x86-64 ISA level v4 build, both SSE and AVX resolvers
are unused.  Check the minimum x86-64 ISA level to exclude the unused
run-time resolvers.