libmvec: further unifdef'ing (LIBMVEC_SO_BUILD)

*** 27,41 ****
   */
  
          .file   "__vcos_ultra3.S"
  
  #include "libm.h"
- #if defined(LIBMVEC_SO_BUILD)
          .weak   __vcos
          .type   __vcos,#function
          __vcos = __vcos_ultra3
- #endif
  
          RO_DATA
          .align  64
  constants:
          .word   0x42c80000,0x00000000   ! 3 * 2^44
--- 27,39 ----