Avoid some binary searches.

In here we are iterating relocations in order, so we can do the same
with the pieces of .eh_frame and avoid a binary search.

The link times I got with this patch were:

firefox
  master 7.22977811
  patch  7.141041442 0.987726225252
chromium
  master 4.478966851
  patch  4.506602207 1.00617002914
chromium fast
  master 1.894713371
  patch  1.866446889 0.98508139414
the gold plugin
  master 0.386193907
  patch  0.382374918 0.990111213743
clang
  master 0.654849589
  patch  0.647899815 0.989387220949
llvm-as
  master 0.037212718
  patch  0.036858172 0.990472450843
the gold plugin fsds
  master 0.410876711
  patch  0.407418613 0.991583611562
clang fsds
  master 0.734623069
  patch  0.728237526 0.991307728726
llvm-as fsds
  master 0.033446197
  patch  0.03302833 0.987506292569
scylla
  master 3.38134402
  patch  3.414188846 1.00971354166

llvm-svn: 276108