ifunc.mac: the ilog2 warning may want to be both ceil and floor

There is no reason why the warning-generating ilog2 has to be only the
floor variant.  However, I am pretty sure we can simply implement the
ilog2cw() as a macro only; we can always fix that if that turns out to
be incorrect.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
diff --git a/doc/changes.src b/doc/changes.src
index b6c987c..73d84eb 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -7,7 +7,6 @@
 The NASM 2 series supports x86-64, and is the production version of NASM
 since 2007.
 
-
 \S{cl-2.12.02} Version 2.12.02
 
 \b Fix preprocessor errors, especially \c{%error} and \c{%warning},
@@ -27,6 +26,9 @@
    macro, display the file and line numbers for the expanded macros.
    Macros defined with \c{.nolist} do not get displayed.
 
+\b Add macros \c{ilog2fw()} and \c{ilog2cw()} to the \c{ifunc} macro
+   package.  See \k{ilog2}.
+
 
 \S{cl-2.12.01} Version 2.12.01