[ELF] - Simplify allocateHeaders(). NFC.
[ELF] - Simplify allocateHeaders(). NFC.

* Return type changed to void, because it was unused.
* std::find_if -> llvm::find_if

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@307039 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld