After the growth of various dependencies, the added weight of a C++
toolchain has become relatively small. I no longer feel it's worth
including as a separate variant.
As of GDB 13.1, gdb.exe contains data triggering a bug in x64 Explorer
zip integration at last as far back as Windows 7. After recompressing
with advzip, gdb.exe extraction fails with 0x80004005 "Unspecified
error". This happens with both 32-bit and 64-bit gdb.exe regardless of
compiler flags. No other zip program has trouble with this file.
Until this is resolved, give up on advzip and tell zip to use -9. Also
renamed the build script option from -q (quick) to -O (optimize) and
disable its use by default.
