[testsuite] [x86] vect-simd-clone-1[678]e.c adjust

[testsuite] [x86] vect-simd-clone-1[678]e.c adjust

Since r13-6296, we haven't got 4 simdclone calls for these tests on
ia32 without avx_runtime.  With avx_runtime, we get 3 such calls even
on ia32, but we didn't test for anything on ia32 with avx_runtime.
Adjust and simplify the expectations and comments.

for  gcc/testsuite/ChangeLog

	* gcc.dg/vect/vect-simd-clone-16e.c: Expect fewer calls on ia32.
	* gcc.dg/vect/vect-simd-clone-17e.c: Likewise.
	* gcc.dg/vect/vect-simd-clone-18e.c: Likewise.