Thanks to nobu for pointing this out. This is a YJIT file so shouldn't
have ZJIT stuff in it. ZJIT doesn't support building on BSDs yet.

Fix: 92b218fbc379fe85792eb060b71520e271971335

Rust 1.58.0 unfortunately doesn't provide facilities to control symbol
visibility/presence, but we care about controlling the list of
symbols exported from libruby-static.a and libruby.so.

This commit uses `ld -r` to make a single object out of rustc's
staticlib output, libyjit.a. This moves libyjit.a out of MAINLIBS and adds
libyjit.o into COMMONOBJS, which obviates the code for merging libyjit.a
into libruby-static.a. The odd appearance of libyjit.a in SOLIBS is also
gone.

To filter out symbols we do not want to export on ELF platforms, we use
objcopy after the partial link. On darwin, we supply a symbol list to
the linker which takes care of hiding unprefixed symbols.

[Bug #19255]

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

This add support for bmake, which should allow building with
`configure --enable-yjit` for the BSDs. Tested on FreeBSD 13 and
on macOS with `configure MAKE=bmake` on a case-sensitive file system.

It works by including a fragment into the Makefile through the configure
script, similar to common.mk. It uses the always rebuild approach to
keep build system changes minimal.