testsuite: [aarch64] Fix aarch64/advsimd-intrinsics/v{trn,uzp,zip}_half.c

testsuite: [aarch64] Fix aarch64/advsimd-intrinsics/v{trn,uzp,zip}_half.c

Since r11-3402 (g:65c9878641cbe0ed898aa7047b7b994e9d4a5bb1), the
vtrn_half, vuzp_half and vzip_half started failing with

vtrn_half.c:76:17: error: redeclaration of 'vector_float64x2' with no linkage
vtrn_half.c:77:17: error: redeclaration of 'vector2_float64x2' with no linkage
vtrn_half.c:80:17: error: redeclaration of 'vector_res_float64x2' with no linkage

This is because r11-3402 now always declares float64x2 variables for
aarch64, leading to a duplicate declaration in these testcases.

The fix is simply to remove these now useless declarations.

These tests are skipped on arm*, so there is no impact on that target.

2020-09-25  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	PR target/71233
	* gcc.target/aarch64/advsimd-intrinsics/vtrn_half.c: Remove
	declarations of vector, vector2, vector_res for float64x2 type.
	* gcc.target/aarch64/advsimd-intrinsics/vuzp_half.c: Likewise.
	* gcc.target/aarch64/advsimd-intrinsics/vzip_half.c: Likewise.

(cherry picked from commit 8c775bf447e190024fa08c55e38db94dd013a393)