This is needed because in libucontext.h we include "libucontext/bits.h".
We therefore need to have bits.h in somepath/libucontext/bits.h. In the
Makefile, somepath/freestanding/bits.h was copied to the right path but
in the meson build system, the include copy happens at the end.
this is not idiomatic, and should not be done (and it did not even
work in the first place); meson is capable of building both
libraries via library() and then you can choose on commandline
it defaults to only shared, but we want both out of box, so specify
that