test: avoid malloc() in threadpool test
test: avoid malloc() in threadpool test

Stack-allocate the `uv_loop_t` instance, no reason to heap-allocate it.

PR-URL: https://github.com/libuv/libuv/pull/1634
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso