Fix an incorrect identifier

[sylvestre.ledru]

Summary

EIEIO is not a correct declaration and breaks the build under Debian HURD.
Instead, E_IEIO is used.

http://www.gnu.org/software/libc/manual/html_node/Reserved-Names.html
Some additional classes of identifier names are reserved for future
extensions to the C language or the POSIX.1 environment. While using
these names for your own purposes right now might not cause a problem,
they do raise the possibility of conflict with future versions of the C
or POSIX standards, so you should avoid these names.
...
Names beginning with a capital ‘E’ followed a digit or uppercase letter
may be used for additional error code names. See Error Reporting.

Reported here:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=776965
And patch wrote by Svante Signell
With this patch, LLVM, Clang & LLDB build under Debian HURD:
https://buildd.debian.org/status/fetch.php?pkg=llvm-toolchain-3.6&arch=hurd-i386&ver=1%3A3.6~%2Brc2-2&stamp=1423040039

[hfinkel]

LGTM, but please make it EnforceIEIO -- I'm against adding arbitrary underscores, but making it more descriptive is okay ;) -- Also, add a comment explaining the naming constraint.

lib/Target/PowerPC/PPCInstrInfo.td

 def ICBI : XForm_1a<31, 982, (outs), (ins memrr:$src),
                     "icbi $src", IIC_LdStICBI, []>;
 
-def EIEIO : XForm_24_eieio<31, 854, (outs), (ins),
+def E_IEIO : XForm_24_eieio<31, 854, (outs), (ins),
                            "eieio", IIC_LdStLoad, []>;
 
 def WAIT : XForm_24_sync<31, 62, (outs), (ins i32imm:$L),