23.x.x release candidate testing

Notes from testing 21.2.21 are in #621 (closed)

Test platforms (wishlist):

• cygwin / gcc / x86-64
• msys2 / mingw32
• msys2 / mingw64
• msvc / vscc
• linux / gcc,clang / x86,x86-64,armv7h,arm64
• unix (freebsd, netbsd, openbsd) / gcc / x86-64
• darwin (OSX) / gcc, clang
• android / gcc / armv7h,arm64
• ios / arm64
• haiku / gcc
• emscripten (may be tricky, optional)

What should be tested:

All platforms (if possible):

• internal tests (make check)
• ansi-tests

Only on linux:

• cl-bench
• closer-mop tests
• maxima tests
• cl-test-grid (last release vs release candidate)
• sbcl cross compile

Configure options (test all of these at least on linux/gcc/x86-64, other platforms are optional):

• --with-cxx=yes
• --with-cmp=no
• --with-sse=yes
• --enable-gengc
• --enable-precisegc
• --disable-threads
• --disable-unicode
• --disable-c99complex
• --disable-smallcons
• --with-dffi=no
• --with-fpe=no
• --with-ieee-fp=no