gdb/testsuite: Update gdb.base/so-impl-ld.exp

gdb.base/so-impl-ld.exp was setup assuming that the compiler would add
epilogue information and that GDB would stop in the } line.  This would
make clang tests fail like so:

 step^M
 solib_main (arg=10000) at ../../../common/git-repos/binutils-gdb/gdb/testsuite/gdb.base/solib1.c:7^M
 7|__  return arg*arg;|__|___/* HERE */^M
 (gdb) PASS: gdb.base/so-impl-ld.exp: step into solib call
 next^M
 main () at ../../../common/git-repos/binutils-gdb/gdb/testsuite/gdb.base/so-impl-ld.c:22^M
 22|_  return 0;^M
 (gdb) FAIL: gdb.base/so-impl-ld.exp: step in solib call
 next^M
 0x00007ffff7cef560 in __libc_start_call_main () from /lib64/libc.so.6^M
 (gdb) FAIL: gdb.base/so-impl-ld.exp: step out of solib call

This patch changes it so solib_main has 2 lines where GDB can stop
regardless of compiler choices, and updates the exp file to
generically deal with unknown number of steps until leaving that
function.

gdb/testsuite/gdb.base/so-impl-ld.exp

@@ -56,21 +56,12 @@ gdb_test "step" "solib_main .arg=10000. at.*${libfile}.c:${decimal}.* HERE .*" \
 
 # Verify that we can step within the shlib call.
 #
-gdb_test "next" "${decimal}\[ \t\]*\}.* STEP .*" "step in solib call"
+gdb_test "next" "${decimal}\[ \t\]*return ans;.* STEP .*" "step in solib call"
 
 # Verify that we can step out of the shlib call, and back out into
 # the caller.
 #
-gdb_test_multiple "next" "step out of solib call" {
-    -re "0x\[0-9a-f\]*\[ \t\]*9\[ \t\]*.*$gdb_prompt $" {
-	gdb_test "next" \
-	    "main .. at.*so-impl-ld.c:22.*" \
-	    "step out of solib call"
-    }
-    -re "main .. at.*so-impl-ld.c:22.*$gdb_prompt $" {
-	pass "step out of solib call"
-    }
-}
+gdb_step_until ".*main .. at.*return 0;.*" "step out of solib call"
 
 gdb_exit
 return 0

gdb/testsuite/gdb.base/solib1.c

@@ -4,5 +4,6 @@ extern "C"
 int
 solib_main (int arg)
 {
-  return arg*arg;		/* HERE */
-}				/* STEP */
+  int ans = arg*arg;		/* HERE */
+  return ans;			/* STEP */
+}