Implement ifunc support for static executables.

A static executable is almost entirely statically relocated by the
linker, with the exception of IRELATIVE relocations, which must be
resolved by libc by enumerating the relocations using the special
linker-defined symbols __rela?_iplt_{start,end}. This patch implements
ifunc support by enumerating the relocations in this way.

Bug: 112482891
Test: /data/nativetest{,64}/bionic-unit-tests-static/bionic-unit-tests-static on walleye_hwasan-userdebug
Change-Id: Ia5522a190da0b86e095b141d5d4e68dd7dd4b695