math/sleef: fix build on powerpc64

[pkubaj]

Summary

Altivec needs {} for vectors instead of ().
lib/libsleefgnuabi.so is not built on powerpc64.

PR: 239468

[mat]

math/sleef/Makefile

31

ARCH is defined after bsd.port.options.mk, no need for the pre/post.

32

This is badly named, it should be NO_PPC64, as it removes things on PPC64, not adds them.

[pkubaj]

Use bsd.port.options.mk and set NO_PPC64.