Original patch from H.J. Lu, as reported there:
http://www.nabble.com/PATCH:-Use-short-for-fnstsw-td14775171.html

fnstsw stores 16bit into %ax. The upper 16bit of %eax is unchanged.
The new assembler (binutils-2.18.50.0.4 and up) will disallow "fnstsw %eax".

diff -dur glibc-2.6.1.orig/sysdeps/i386/fpu/ftestexcept.c glibc-2.6.1/sysdeps/i386/fpu/ftestexcept.c
--- glibc-2.6.1.orig/sysdeps/i386/fpu/ftestexcept.c	2004-03-05 11:14:48.000000000 +0100
+++ glibc-2.6.1/sysdeps/i386/fpu/ftestexcept.c	2008-06-24 10:56:14.000000000 +0200
@@ -26,7 +26,7 @@
 int
 fetestexcept (int excepts)
 {
-  int temp;
+  short temp;
   int xtemp = 0;
 
   /* Get current exceptions.  */