elf.h: add typedefs for Elf64_Relr and Elf32_Relr

These were overlooked when DT_RELR was added in commit
d32dadd60efb9d3b255351a3b532f8e4c3dd0db1, potentially breaking
software that treats presence of the DT_RELR macro as implying they
exist.

include/elf.h

@@ -558,6 +558,11 @@ typedef struct {
 
 
 
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
+
+
 #define ELF32_R_SYM(val)		((val) >> 8)
 #define ELF32_R_TYPE(val)		((val) & 0xff)
 #define ELF32_R_INFO(sym, type)		(((sym) << 8) + ((type) & 0xff))