Add ELF.h and Dwarf.h from LLVM for gdbjit feature implementation. (#6383)

Files were copied from http://llvm.org/git/llvm.git repo, commit: 8b47c17a53d683f313eaaa93c4a53de26d8fcba5

Author: lucenticus

THIRD-PARTY-NOTICES

@@ -39,3 +39,49 @@ TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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