archivers/gtar: fix build on i386

Override a hidden safety check that stops the build on platforms
that are not Y2038 safe.  FreeBSD/i386 still has a 32-bit time_t.

PR:		272622
Reported by:	cy

archivers/gtar/Makefile

@@ -17,6 +17,8 @@ USES=		charsetfix cpe iconv:${STATIC_ARGS} localbase tar:xz
 CPE_VENDOR=	gnu
 GNU_CONFIGURE=	yes
 CONFIGURE_ARGS=	--program-prefix=g
+# unbuckle safety belt: FreeBSD/i386 still has 32-bit time_t
+CONFIGURE_ARGS+=--disable-year2038
 CONFIGURE_ENV=	DEFAULT_RMT_COMMAND=/etc/rmt
 # supply result to skip a test that will abort configure if run as root
 CONFIGURE_ENV+=	gl_cv_func_mknod_works=yes