Update ELF/constants.jl (#48)

* Update ELF/constants.jl

Point to glibc where these constants live.

* Update src/ELF/constants.jl

Co-authored-by: Mosè Giordano <765740+giordano@users.noreply.github.com>

---------

Co-authored-by: Mosè Giordano <765740+giordano@users.noreply.github.com>

Author: eschnett

src/ELF/constants.jl

@@ -1,3 +1,7 @@
+# These constants are in glibc and llvm:
+# * https://github.com/bminor/glibc/blob/969d7cf89966d55fbf0732ae7bc0949a970c837d/elf/elf.h
+# * https://github.com/llvm/llvm-project/blob/b2d7312d52f299a2f854c673796ad1a699e0d79f/llvm/include/llvm/BinaryFormat/ELF.h
+
 # e_ident[EIBCLASS]
 const ELFCLASSNONE = 0 #Invalid class
 const ELFCLASS32 = 1 #32-bit objects