libmvec: further unifdef'ing (LIBMVEC_SO_BUILD)

@@ -27,15 +27,13 @@
  */
 
         .file   "__vsin_ultra3.S"
 
 #include "libm.h"
-#if defined(LIBMVEC_SO_BUILD)
         .weak   __vsin
         .type   __vsin,#function
         __vsin = __vsin_ultra3
-#endif
 
         RO_DATA
         .align  64
 constants:
         .word   0x42c80000,0x00000000   ! 3 * 2^44