aarch64: use configure check for assembly ELF directives support
* configure.ac (gcry_cv_gcc_asm_elf_directives): New check. (HAVE_GCC_ASM_ELF_DIRECTIVES): New 'config.h' macro. * cipher/asm-common-aarch64.h (ELF): Change feature macro check from __ELF__ to HAVE_GCC_ASM_ELF_DIRECTIVES.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>