base: (linux) arch flags are not recognized by linux compilers

[kencu (Ken)]

On Ubuntu, gcc errors when it is given an arch flag on the build line. The darwin builds of gcc accepts arch but the linux version does not.

clang accepts the arch flags, but doesn't use them, and issues a warning that the flag is unrecognized. This can generate configure errors.

The archflags can be manually cleared in the portfiles by setting them all to empty strings, like we do in the gcc Portfiles.

In base, I tried overriding portconfigure::arch_flag_supported to return no on linux, but that then resulted in another error that said (something like)

error: cc has no archflags