Add '_' in the match pattern.

I was looking at GDB testcase results for arm-eabi target with qemu and
noticed that register groups returned by the qemu can have '_' in the
name e.g. 'cp_regs'. The reggroups.exp fails to recognize that as group
name. Fixed by adding '_' in the pattern.

2018-09-20  Hafiz Abid Qadeer  <abidh@codesourcery.com>

	gdb.base/reggroups.exp (fetch_reggroups): Add '_' in match pattern.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2018-09-20  Hafiz Abid Qadeer  <abidh@codesourcery.com>
+
+	gdb.base/reggroups.exp (fetch_reggroups): Add '_' in match pattern.
+
 2018-09-18  Sandra Loosemore  <sandra@codesourcery.com>
 
 	* gdb.base/complete-empty.exp: Skip tab-completion tests if

gdb/testsuite/gdb.base/reggroups.exp

@@ -43,7 +43,7 @@ proc fetch_reggroups {test} {
 	-re "^ Group\[ \t\]+Type\[ \t\]+\r\n" {
 	    exp_continue
 	}
-	-re "^ (\[0-9a-zA-Z-\]+)\[ \t\]+(user|internal)\[ \t\]+\r\n" {
+	-re "^ (\[_0-9a-zA-Z-\]+)\[ \t\]+(user|internal)\[ \t\]+\r\n" {
 	    lappend reggroups $expect_out(1,string)
 	    exp_continue
 	}