boost: refresh GCC options in Makefile

boost: refresh GCC options in Makefile

this Makefile still used `CONFIG_GCC_USE_VERSION_*` to select various
compilation options, for GCC versions that are antiquated

convert to parsing the major from the `CONFIG_GCC_VERSION` which will
always exist and can also be used with range logic

intent seemed to be:
* `-std=gnu++20` for "=10" (and newer, probably)
* `-std=gnu++14` for "=5"
* `-std=gnu++17` for "not =10 and not =5"

GCC 11 or 12 would likely revert to the default (6 through 9) option
with those, because 10 was the newest at the time, and 11 and 12 are
"not =10 and not =5"

probably the GCC 5 support could be removed, not sure about 9 and 10

Signed-off-by: Tony Butler <spudz76@gmail.com>