Skip PR binutils/23494 tests for nacl targets

Skip PR binutils/23494 tests for nacl targets

PR binutils/23494 tests pass "-O elf64-x86-64" and "-O elf32-x86-64"
to objcopy which may not supported for nacl targets.  This patch skips
these tests for nacl targets.

	* testsuite/binutils-all/x86-64/pr23494a-x32.d: Skip nacl
	targets.
	* testsuite/binutils-all/x86-64/pr23494a.d: Likewise.
	* testsuite/binutils-all/x86-64/pr23494b-x32.d: Likewise.
	* testsuite/binutils-all/x86-64/pr23494b.d: Likewise.
	* testsuite/binutils-all/x86-64/pr23494c-x32.d: Likewise.
	* testsuite/binutils-all/x86-64/pr23494c.d: Likewise.
	* testsuite/binutils-all/x86-64/pr23494d-x32.d: Likewise.
	* testsuite/binutils-all/x86-64/pr23494d.d: Likewise.