Use autoconf to detect function attributes; some compilers like Sun CC
do support some gcc-style attributes, but don't define __GNUC__. Also
-U__STRICT_ANSI__ already in configure.ac so our tests match what we
might eventually encounter.
Add const_func and pure_func attributes.
Decorate functions in nasmlib.h with const_func and pure_func.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
8b19083483