powerpc: fix conflicting definitions with newer Linux kernel

libc/sysdeps/linux/powerpc/sys/procfs.h

@@ -34,7 +34,7 @@ __BEGIN_DECLS
 /* These definitions are normally provided by ucontext.h via
    asm/sigcontext.h, asm/ptrace.h, and asm/elf.h.  Otherwise we define
    them here.  */
-#ifndef __PPC64_ELF_H
+#if !defined __PPC64_ELF_H && !defined _ASM_POWERPC_ELF_H
 #define ELF_NGREG       48      /* includes nip, msr, lr, etc. */
 #define ELF_NFPREG      33      /* includes fpscr */
 #if __WORDSIZE == 32