Fix autoconf 2.68 warning.
Fix autoconf 2.68 warning.

The first argument of AC_COMPILE_IFELSE needs to be wrapped with
AC_LANG_SOURCE.

techkey/nasm,projedi/nasm,Distrotech/nasm,turingstudio/nasm,projedi/nasm,projedi/nasm,techkey/nasm,Distrotech/nasm,turingstudio/nasm,letolabs/nasm,Distrotech/nasm,turingstudio/nasm,Distrotech/nasm,techkey/nasm,projedi/nasm,letolabs/nasm,letolabs/nasm,techkey/nasm,turingstudio/nasm,techkey/nasm,projedi/nasm