Use general instruction/stack pointer convenience method instead of manually

src/google_breakpad/common/minidump_cpu_ppc.h

 /* Copyright (c) 2006, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 122 matching lines @@
   uint32_t              mq;      /* Multiply/Quotient (PPC 601, POWER only) */
   uint32_t              vrsave;  /* Vector save */
 
   /* float_save and vector_save aren't present in ppc_thread_state, but
    * are represented in separate structures that still define a thread's
    * context. */
   MDFloatingSaveAreaPPC float_save;
   MDVectorSaveAreaPPC   vector_save;
 } MDRawContextPPC;  /* Based on ppc_thread_state */
 
+/* Indices into gpr for registers with a dedicated or conventional purpose. */
+enum MDPPCRegisterNumbers {
+  MD_CONTEXT_PPC_REG_SP = 1
+};
+
 #if defined(__SUNPRO_C) || defined(__SUNPRO_CC)
 #pragma pack(0)
 #else
 #pragma pack(pop)
 #endif
 
 /* For (MDRawContextPPC).context_flags.  These values indicate the type of
  * context stored in the structure.  MD_CONTEXT_PPC is Breakpad-defined.  Its
  * value was chosen to avoid likely conflicts with MD_CONTEXT_* for other
  * CPUs. */
 #define MD_CONTEXT_PPC                0x20000000
 #define MD_CONTEXT_PPC_BASE           (MD_CONTEXT_PPC | 0x00000001)
 #define MD_CONTEXT_PPC_FLOATING_POINT (MD_CONTEXT_PPC | 0x00000008)
 #define MD_CONTEXT_PPC_VECTOR         (MD_CONTEXT_PPC | 0x00000020)
 
 #define MD_CONTEXT_PPC_FULL           MD_CONTEXT_PPC_BASE
 #define MD_CONTEXT_PPC_ALL            (MD_CONTEXT_PPC_FULL | \
                                        MD_CONTEXT_PPC_FLOATING_POINT | \
                                        MD_CONTEXT_PPC_VECTOR)
 
 #endif /* GOOGLE_BREAKPAD_COMMON_MINIDUMP_CPU_PPC_H__ */