[gdb/testsuite] Fix gdb.base/infcall-exec.exp for remote target

When running test-case gdb.base/infcall-exec.exp with target board
remote-gdbserver-on-localhost (using REMOTE_TARGET_USERNAME) we run into:
...
(gdb) call (int) execlp ("$outputs/gdb.base/infcall-exec/infcall-exec2", \
  "$outputs/gdb.base/infcall-exec/infcall-exec2", (char *)0)^M
$1 = -1^M
(gdb) FAIL: gdb.base/infcall-exec.exp: call execlp
...

Fix this by using just:
...
(gdb) call (int) execlp ("infcall-exec2", "infcall-exec2", (char *)0)^M
...
and using putenv ("PATH=...") to allow infcall-exec to exec infcall-exec2
if it's available alongside.

Also fix the exec name in the test-case, such that we can successfully
run the test-case:
...
$ ./outputs/gdb.base/infcall-exec/infcall-exec
PATH SETTING: 'PATH=./outputs/gdb.base/infcall-exec'
$
...

Tested on x86_64-linux.

Co-Authored-by: Ivan Tetyushkin <ivan.tetyushkin@syntacore.com>

gdb/testsuite/gdb.base/infcall-exec.c

@@ -16,13 +16,57 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <unistd.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <string.h>
+#include <stdio.h>
+#include <assert.h>
+
+static void
+set_path (int argc, char ** argv)
+{
+  if (argc < 1)
+    return;
+
+  char path[PATH_MAX];
+  strcpy (path, argv[0]);
+  int len = strlen (path);
+
+  /* Make a path name out of an exec name.  */
+  int i;
+  for (i = len - 1; i >= 0; i--)
+    {
+      char c = path[i];
+      if (c == '/' || c == '\\')
+	{
+	  path[i] = '\0';
+	  break;
+	}
+    }
+  len = i;
+
+  if (len == 0)
+    return;
+
+  /* Prefix with "PATH=".  */
+  const char *prefix = "PATH=";
+  int prefix_len = strlen (prefix);
+  memmove (path + prefix_len, path, len);
+  path[prefix_len + len] = '\0';
+  memcpy (path, prefix, prefix_len);
+
+  printf ("PATH SETTING: '%s'\n", path);
+  putenv (path);
+}
 
 int
 main (int argc, char ** argv)
 {
-  const char *prog = "inf-exec2";
+  set_path (argc, argv);
+  const char *prog = "infcall-exec2";
 
-  execlp (prog, prog, (char *) 0);
+  int res = execlp (prog, prog, (char *) 0); /* break here */
+  assert (res != -1);
 
   return 0;
 }

gdb/testsuite/gdb.base/infcall-exec.exp

@@ -32,13 +32,21 @@ if {[gdb_compile $srcdir/$subdir/$srcfile2 $binfile2 executable debug] != ""} {
     return -1
 }
 
+if { [is_remote target] } {
+    set binfile2 [gdb_remote_download target $binfile2]
+}
+
 clean_restart $binfile
 
 if {![runto_main]} {
     return -1
 }
 
-set expected_result "process $decimal is executing new program: $binfile2"
+set linenr [gdb_get_line_number "break here"]
+gdb_breakpoint $linenr
+gdb_continue_to_breakpoint "Ensure PATH is set" ".* break here .*"
+
+set expected_result "process $decimal is executing new program: \[^\r\n\]*$binfile2"
 append expected_result "\[\r\n\]+.*"
 append expected_result "Breakpoint 1, main .*at .*$srcfile2:$decimal"
 append expected_result ".*"