Prevent MSVC from optimizing away tls_callback (resolves #318)
Prevent MSVC from optimizing away tls_callback (resolves #318)

AndroidExternal/jemalloc,cpeterso/jemalloc,jemalloc/jemalloc-cmake,jemalloc/jemalloc-cmake,8l/jemalloc,cpeterso/jemalloc,cpeterso/jemalloc,8l/jemalloc,jemalloc/jemalloc-cmake,AndroidExternal/jemalloc,8l/jemalloc,leebaok/jemalloc-4.2.1-readcode,wqfish/jemalloc,wqfish/jemalloc,glandium/jemalloc,leebaok/jemalloc-4.2.1-readcode,8l/jemalloc,jemalloc/jemalloc-cmake,wqfish/jemalloc,leebaok/jemalloc-4.2.1-readcode,AndroidExternal/jemalloc,AndroidExternal/jemalloc,glandium/jemalloc,glandium/jemalloc,glandium/jemalloc,wqfish/jemalloc,leebaok/jemalloc-4.2.1-readcode,cpeterso/jemalloc,wqfish/jemalloc