[LTO] Include in .symtab/.dynsym symbols introduced by optimizations.

Some optimizations, e.g. SimplifyLibCalls, can replace functions with
others as part of the lowering, e.g. printf => puts.
The new symbols don't have the isUsedInRegularObj flag set so they
don't get included in the final symbol table (and dynamic symbol
table), and the dynamic linker gets confused. Include  them as a fix.

Differential Revision: http://reviews.llvm.org/D18357

llvm-svn: 264688