lang/sbcl: fix build on i386 and powerpc64*

SB-ALIEN:ALIEN-FUNCALL-INTO is exported unconditionally and documented by
the new SB-MANUAL contrib, but the function itself is #+(or x86-64 arm64),
so generating the Texinfo sources dies with an undefined-function error on
i386, powerpc64 and powerpc64le.

Obtained from: https://github.com/sbcl/sbcl/commit/7ee531486117197e89c95507a5919ef08f36220b