Convert from libc mutex to osv mutex.

For some reason this didn't work.  Also make sure to clean out so
files in make clean so this gets noticed.

An off-by-one meant the the object pool for sizes above half a page was
not initialized.

Add a new hello_world test payload that can be used to test OSv functionality
more fine grained.  For now the binary loaded remains hardcoded in loader.cc
and still defaults to libjvm.so.

Implemented the wrong prototype.

Just forward the formatted string to debug() for now.  This allows
bringing up a trivial hello world test payload.

Usedful for implementing stdio.

If we already have a clean tree xargs won't find any object files.
Add the -f argument to rm so that it doesn't complain about the lack
of arguments.

If we can't find a symbol, return null.  This occurs with libjsig symbols,
which need not be loaded.

We captured the precision function (which either returns an inline precision
or from an argument, via *12$) by value, then tries to update it to set a
default precision.  But since we captured it already, the update had no effect.

Change the code to return the precision function and store it in the fragment
instead.