libbpf: fix powerpc's stack register definition in bpf_tracing.h

retsnoop's build on powerpc (ppc64le) architecture ([0]) failed due to
wrong definition of PT_REGS_SP() macro. Looking at powerpc's
implementation of stack unwinding in perf_callchain_user_64() clearly
shows that stack pointer register is gpr[1].

Fix libbpf's definition of __PT_SP_REG for powerpc to fix all this.

  [0] https://kojipkgs.fedoraproject.org/work/tasks/1544/137921544/build.log

Fixes: 138d615 ("samples/bpf: Enable powerpc support")
Cc: Naveen N Rao <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>

Author: anakryiko

tools/lib/bpf/bpf_tracing.h

@@ -311,7 +311,7 @@ struct pt_regs___arm64 {
 #define __PT_RET_REG regs[31]
 #define __PT_FP_REG __unsupported__
 #define __PT_RC_REG gpr[3]
-#define __PT_SP_REG sp
+#define __PT_SP_REG gpr[1]
 #define __PT_IP_REG nip
 
 #elif defined(bpf_target_sparc)