Add IFUNC support for arm64 and IRELATIVE reloc

 There are number of changes in the way IFUNC related relocations are done:
 1. IRELATIVE relocations are now supported for x86/x86_64 and arm64.
 2. IFUNC relocations are now relying on static linker to generate
    them in correct order - this removes necessety of additional
    relocation pass for ifuncs.
 3. Related to 2: rela?.dyn relocations are preformed before .plt ones.
 4. Ifunc are resolved on symbol lookup this approach allowed to avoid
    mprotect(PROT_WRITE) call on r-x program segments.

Bug: 17399706
Bug: 17177284
Change-Id: I414dd3e82bd47cc03442c5dfc7c279949aec51ed
diff --git a/libc/arch-x86/include/machine/elf_machdep.h b/libc/arch-x86/include/machine/elf_machdep.h
index 442c561..4bce933 100644
--- a/libc/arch-x86/include/machine/elf_machdep.h
+++ b/libc/arch-x86/include/machine/elf_machdep.h
@@ -59,5 +59,6 @@
 #define	R_386_TLS_GOTDESC	39
 #define	R_386_TLS_DESC_CALL	40
 #define	R_386_TLS_DESC		41
+#define	R_386_IRELATIVE		42
 
 #define	R_TYPE(name)	__CONCAT(R_386_,name)