ELF: Support detection of relocation errors during processing

At the moment errors in relocation processing such as out of range
values are not detected or at best trapped by asserts which will not
be present in release builds. This patch adds support for checking
error return values from applyRelocation() calls and printing an
appropriate error message. It also adds support for printing multiple
errors rather than just the first one.

llvm-svn: 226557