ADD8TLS, a variant of add instruction used for initial-exec TLS,
currently accepts r0 as a source register. While add itself supports
r0 just fine, linker can relax it to a local-exec sequence, converting
it to addi - which doesn't support r0.
Differential Revision: http://reviews.llvm.org/D19193
llvm-svn: 267388
Marcin Koscielnicki