[ELF] .eh_frame: remove config->wordsize padding

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).