expose TSVTX unconditionally in tar.h
as noted in Austin Group issue #1236, the XSI shading for TSVTX is
misplaced in the html version of the standard; it was only supposed to
be on the description text. the intent was that the definition always
be visible, which is reflected in the pdf version of the standard.
this reverts commits d93c0740d86aaf7043e79b942a6c0b3f576af4c8 and
729fef0a9358e2f6f1cd8c75a1a0f7ee48b08c95.
Rich Felker