LibC+LibELF: Implement support for the dl_iterate_phdr helper

This helper is used by libgcc_s to figure out where the .eh_frame sections
are located for all loaded shared objects.

Userland/Libraries/LibC/CMakeLists.txt

@@ -13,6 +13,7 @@ set(LIBC_SOURCES
     ioctl.cpp
     libcinit.cpp
     libgen.cpp
+    link.cpp
     locale.cpp
     malloc.cpp
     mman.cpp