Fix test step-and-next-inline.cc

The test expect the runto_main to stop at the first line of the function.
Depending on the optimization level, gdb may stop in the prolog or after
the prolog at the first line.  To ensure the test stops at the first line
of main, have it explicitly stop at a break point on the first line of the
function.

On PowerPC, the test passes when compiled with no optimization but fails
with all levels of optimization due to gdb stopping in the prolog.

gdb/testsuite/gdb.cp/step-and-next-inline.cc

@@ -61,6 +61,6 @@ tree xx;
 int
 main()
 {
-  get_alias_set (&xx);
+  get_alias_set (&xx);  /* Beginning of main */
   return 0;
 } // main

gdb/testsuite/gdb.cp/step-and-next-inline.exp

@@ -58,7 +58,9 @@ proc do_test { use_header } {
 
     with_test_prefix $prefix {
 
-    if ![runto_main] {
+    set main_location [gdb_get_line_number "Beginning of main" $srcfile]
+
+    if ![runto $main_location qualified] {
 	return
     }