i386: Optimize pinsrq of 0 with index 1 into movq [PR94866]

i386: Optimize pinsrq of 0 with index 1 into movq [PR94866]

Add new pattern involving vec_merge RTX that is produced by combine from the
combination of sse4_1_pinsrq and *movdi_internal:

    7: r86:DI=0
    8: r85:V2DI=vec_merge(vec_duplicate(r86:DI),r87:V2DI,0x2)
      REG_DEAD r87:V2DI
      REG_DEAD r86:DI
Successfully matched this instruction:
(set (reg:V2DI 85 [ a ])
    (vec_merge:V2DI (reg:V2DI 87)
        (const_vector:V2DI [
                (const_int 0 [0]) repeated x2
            ])
        (const_int 1 [0x1])))

	PR target/94866

gcc/ChangeLog:

	* config/i386/sse.md (*sse2_movq128_<mode>_1): New insn pattern.

gcc/testsuite/ChangeLog:

	* g++.target/i386/pr94866.C: New test.