Add sw_64 CPU architecture support

[Verney7]

In this commit, support for a new architecture sw_64 is added to bazel. sw_64 is a new RISC ISA, which is a bit like RISC-V. Though it is a rather new ISA, it has been added to openEuler and openAnolis port since 2020. So supporting this new architecture is meaningful. It's PR is to solve compilation failure on sw_64 architecture.

platforms merge request: platforms#124

Binutils has identified EM_SW64 is 268, I hope bazel can accept this patch. Thanks.

https://en.wikipedia.org/wiki/Sunway_(processor)

More information about sw_64 ISA:

$ uname -m
sw_64
$ gcc -E -dM - < /dev/null|grep __sw_64__
#define __sw_64__ 1
$ gcc -E -dM - < /dev/null|grep BYTE_ORDER
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__

[satyanandak]

@Verney7 Could you please take a look at the failing checks?

[Verney7]

@Verney7 Could you please take a look at the failing checks?

These failing checks seem to be related to this bazelbuild/platforms/#124 not being merged. Can you help me merge this request?

[gregestren]

Just to clarify, this PR is for bazel itself to be buildable for sw_64?