Replace the exclusion list with an allowlist of the architectures
whose libc exports brk/sbrk: amd64, i386, arm and powerpc.
On aarch64, riscv and loongarch libc does not export those symbols
and the test cannot run, so do not build it there. New architectures
now default to not building the test unless brk support is added.
Signed-off-by: Xiaoqiang Zhao <zhaoxiaoqiang007@gmail.com>