Improve test for processor feature om MPX registers test.

Skips the MPX register test in case target is not Intel.
Improves the test for MPX feature making MPX and AVX512
tests more similar in terms of initialization.
Indentation was improved on sample file and final return added
to have_mpx.  On test file identation was improved and
gdb_send was exchanged by gdb_test_multiple.

2015-06-08  Walfred Tedeschi  <walfred.tedeschi@intel.com>

gdb/testsuite
	* gdb.arch/i386-mpx.c: Added final return to the have_mpx
	function and improved indentation.
	* gdb.arch/i386-mpx.exp: Exchanging gdb_send and gdb_expect for
	gdb_test_multiple. Added additional tests to skip the test.

gdb/testsuite/gdb.arch/i386-mpx.c

@@ -46,6 +46,7 @@ have_mpx (void)
        else
 	 return 0;
      }
+  return 0;
 }
 
 int

gdb/testsuite/gdb.arch/i386-mpx.exp

@@ -22,6 +22,11 @@ if { ![istarget i?86-*-*] && ![istarget x86_64-*-* ] } {
 
 standard_testfile
 
+if { ![istarget i?86-*-*] && ![istarget x86_64-*-* ] } {
+    verbose "Skipping x86 MPX tests."
+    return
+}
+
 set comp_flags "-fmpx -I${srcdir}/../nat/"
 
 if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} \
@@ -34,23 +39,23 @@ if ![runto_main] {
     return -1
 }
 
-send_gdb "print have_mpx ()\r"
-gdb_expect {
-    -re ".. = 1\r\n$gdb_prompt " {
-        pass "check whether processor supports MPX"
+set supports_mpx 0
+set test "probe MPX support"
+gdb_test_multiple "print have_mpx()" $test {
+    -re ".. = 1\r\n$gdb_prompt $" {
+        pass $test
+        set supports_mpx 1
     }
-    -re ".. = 0\r\n$gdb_prompt " {
-        verbose "processor does not support MPX; skipping MPX tests"
-        return
-    }
-    -re ".*$gdb_prompt $" {
-        fail "check whether processor supports MPX"
-    }
-    timeout {
-        fail "check whether processor supports MPX (timeout)"
+    -re ".. = 0\r\n$gdb_prompt $" {
+        pass $test
     }
 }
 
+if { !$supports_mpx } {
+    unsupported "processor does not support MPX"
+    return
+}
+
 # Test bndcfg register and bndstatus at startup
 set test_string "\\\{raw = 0x\[0-9a-f\]+, config = \\\{base = \[0-9\]+,\
 reserved = \[0-9\]+, preserved = \[0-9\]+, enabled = \[0-9\]+\\\}\\\}"