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).
glibc/sysdeps/unix/sysv/linux/x86_64/sigaction.c libc.a(sigaction.o) has a CIE
with the augmentation string "zRS". Support 'S' to allow --icf={safe,all}.
Also change some options that have different semantics (cause confusion) in llvm-readelf mode:
-s => -S
-t => --symbols
-sd => --section-data
llvm-svn: 359651
