[ppc64le] Use skip_entrypoint for skip_trampoline_code

ppc64le loses control when stepping between two PLT-called functions inside
a shared library:

29        shlib_second (); /* first-hit */^M
(gdb) PASS: gdb.base/solib-intra-step.exp: first-hit
step^M
^M
Program received signal SIGABRT, Aborted.^M
0x00003fffb7cbe578 in __GI_raise (sig=<optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56^M
56        return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);^M
(gdb) FAIL: gdb.base/solib-intra-step.exp: second-hit
->
29        shlib_second (); /* first-hit */^M
(gdb) PASS: gdb.base/solib-intra-step.exp: first-hit
step^M
shlib_second () at ./gdb.base/solib-intra-step-lib.c:23^M
23        abort (); /* second-hit */^M
(gdb) PASS: gdb.base/solib-intra-step.exp: second-hit

This is because gdbarch_skip_trampoline_code() will resolve the final function
as shlib_second+0 and place there the breakpoint, but ld.so will jump after
the breakpoint - at shlib_second+8 - as it is ELFv2 local symbol optimization:

Dump of assembler code for function shlib_second:
   0x0000000000000804 <+0>:     addis   r2,r12,2
   0x0000000000000808 <+4>:     addi    r2,r2,30668
   0x000000000000080c <+8>:     mflr    r0

Currently gdbarch_skip_entrypoint() has been called in skip_prologue_sal() and
fill_in_stop_func() but that is not enough.  I believe
gdbarch_skip_entrypoint() should be called after every
gdbarch_skip_trampoline_code().

gdb/ChangeLog
2015-09-15  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* linespec.c (minsym_found): Call gdbarch_skip_entrypoint.
	* ppc64-tdep.c (ppc64_skip_trampoline_code): Rename to ...
	(ppc64_skip_trampoline_code_1): ... here.
	(ppc64_skip_trampoline_code): New wrapper function.
	* symtab.c (find_function_start_sal): Call gdbarch_skip_entrypoint.

gdb/testsuite/ChangeLog
2015-09-15  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.opt/solib-intra-step-lib.c: New file.
	* gdb.opt/solib-intra-step-main.c: New file.
	* gdb.opt/solib-intra-step.exp: New file.

gdb/linespec.c

@@ -3570,6 +3570,8 @@ minsym_found (struct linespec_state *self, struct objfile *objfile,
 	  sal.pc = MSYMBOL_VALUE_ADDRESS (objfile, msymbol);
 	  sal.pc = gdbarch_convert_from_func_ptr_addr (gdbarch, sal.pc,
 						       &current_target);
+	  if (gdbarch_skip_entrypoint_p (gdbarch))
+	    sal.pc = gdbarch_skip_entrypoint (gdbarch, sal.pc);
 	}
       else
 	skip_prologue_sal (&sal);