ELF: Include the build ID section in the first page.

At least Linux has the kernel configuration to include the first page
of the executable into core files. We want build ID section to be
included in core files to identify them.

Here is the link to the description about the kernel configuration.

https://github.com/torvalds/linux/blob/097f70b3c4d84ffccca15195bdfde3a37c0a7c0f/fs/Kconfig.binfmt#L46

llvm-svn: 263351