build-sys: fix again UL_SCANF_TYPE_MODIFIER

build-sys: fix again UL_SCANF_TYPE_MODIFIER

This reverts commit c8494d88:
  "build-sys: fix UL_SCANF_TYPE_MODIFIER for icc"

plus fix the check prog, because it found "%as" to be valid on
systems where "%a" is used for float conversion.

icc warns about "%ms" but it works anyways. Our AC_RUN_IFELSE prog
should do it right now regardless of compiler warnings.

Note "%ms" is POSIX.1-2008 standard but still not available on
many systems. Maybe it's time to remove "%as" fallback for old
glibc which is even less portable.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>