PR25882, .gnu.attributes are not checked for shared libraries

[Joseph Myers]

This binutils patch breaks glibc "make check" for big-endian powerpc 
(32-bit and 64-bit).

https://sourceware.org/pipermail/libc-testresults/2020q2/006097.html

Errors of the form:

/scratch/jmyers/glibc-bot/install/compilers/powerpc64-linux-gnu/lib/gcc/powerpc64-glibc-linux-gnu/11.0.0/../../../../powerpc64-glibc-linux-gnu/bin/ld: /scratch/jmyers/glibc-bot/build/glibcs/powerpc64-linux-gnu/glibc/math/test-nldbl-redirect.o uses 64-bit long double, /scratch/jmyers/glibc-bot/build/glibcs/powerpc64-linux-gnu/glibc/math/libm.so.6 uses 128-bit long double

I don't know whether this is a problem with binutils, or it indicates that 
BE powerpc glibc needs to use -mno-gnu-attribute on some files like LE 
does to avoid such errors.

-- 
Joseph S. Myers
joseph@codesourcery.com