[llvm-readobj] - An attemp to fix BB.

BB failed:
http://lab.llvm.org:8011/builders/clang-armv7-linux-build-cache/builds/15062/steps/build%20stage%201/logs/stdio

Error was:
/home/buildslave/buildslave/clang-armv7-linux-build-cache/llvm/tools/llvm-readobj/ELFDumper.cpp:3540:7:
error: non-constant-expression cannot be narrowed from type 'llvm::support::detail::packed_endian_specific_integral<unsigned long long,
llvm::support::endianness::little, 1>::value_type' (aka 'unsigned long long') to 'size_t' (aka 'unsigned int') in initializer list [-Wc++11-narrowing]
      StrTabSec->sh_size};

llvm-svn: 362084