build-many-glibcs.py failures for powerpc

[Joseph Myers]

In tests with mainline GCC and binutils I see:

FAIL: glibcs-powerpc-linux-gnu check
FAIL: glibcs-powerpc-linux-gnu-power4 check
FAIL: glibcs-powerpc64le-linux-gnu check

https://sourceware.org/ml/libc-testresults/2017-q1/msg00026.html

The first two are elf/check-textrel failing for libm.so.  The third is 
elf/check-localplt failing ("Extra PLT reference: libc.so: strncmp").  
There are no such failures for powerpc64 big endian or for soft float / 
e500.  I suppose the first two might be GCC / binutils bugs, given that I 
don't see them with the bot using GCC 6 branch and binutils 2.28 branch.  
I don't know how long any of these failures have been around, since 
previously they'd have been hidden by the warnings causing failures for 
all architectures.

-- 
Joseph S. Myers
joseph@codesourcery.com