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

(cherry picked from commit 9aea164457)

Change-Id: Ie19d900fc203beb93faf8943b0d06d534a6de4ad

libc/arch-arm64/include/machine/elf_machdep.h

@@ -99,6 +99,7 @@
 #define R_AARCH64_RELATIVE              1027    /* Adjust by program base.  */
 #define R_AARCH64_TLS_TPREL64           1030
 #define R_AARCH64_TLS_DTPREL32          1031
+#define R_AARCH64_IRELATIVE             1032
 
 #define R_TYPE(name)        __CONCAT(R_AARCH64_,name)
 

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)

libc/arch-x86_64/include/machine/elf_machdep.h

@@ -46,6 +46,8 @@
 #define R_X86_64_GOTTPOFF	22
 #define R_X86_64_TPOFF32	23
 
+#define R_X86_64_IRELATIVE	37
+
 #define	R_TYPE(name)	__CONCAT(R_X86_64_,name)
 
 #else	/*	!__i386__	*/