For a main thread a thread object is created by the CRT0 before _main gets
called so that _main can already run in a generic environment that, e.g.,
catches stack overflows as a page-fault instead of corrupting the BSS.
Additionally dynamic programs have only one CRT0 - the one of the LDSO -
which does the initialization for both LDSO and program.
ref #989
In the current form, only PROT_READ is supported. This case is emulated
by copying the file content into new allocated backing store. Even
though the performance benefits of mmap-using code will not be
preserved, code that relies on mmap can be executed via the libc_noux
or libc_fs plugins, i.e. lightttpd.
