Linux Standard Base Core Specification says that CIE/FDE is padded to an
addressing unit size boundary, but in practice GNU assembler/LLVM integrated
assembler pad FDE/CIE to 4 and the last FDE to 8 on 64-bit systems.
In addition, GNU ld doesn't pad to 8, so let's drop excess padding, too.
If the assembler provides aligned pieces, the output will be aligned.
Noticed .eh_frame size reduction for 3 executables: 0.3% (chrome), 4.7% (clang),
7.6% (an internal program).
Noticed while testing for an out of tree target. There are probably more tests that should be so marked.
I'm not sure who owns these tests so I've added a few names I recognise from the recent history.
With advice from probinson, ruiu, rafael and dramatically improved by davidb. Thank you all!
Differential Revision: https://reviews.llvm.org/D34685
llvm-svn: 308335
