[gdb/testsuite] Fix gdb.base/watchpoint-reuse-slot.exp with gcc-8

When running test-case gdb.base/watchpoint-reuse-slot.exp with gcc-8 instead
of gcc-7, we have:
...
 (gdb) PASS: $conf: watch *(buf.byte + 0 + 0)@1
 stepi^M
-0x00000000004004b9      34        for (i = 0; i < 100000; i++);^M
+34        for (i = 0; i < 100000; i++);^M
-(gdb) PASS: $conf: stepi advanced
+(gdb) FAIL: $conf: stepi advanced
...
where $conf is "gdb.base/watchpoint-reuse-slot.exp: hw-watch: always-inserted
off: watch x watch: : width 1, iter 0: base + 0".

This is due to the fact that gcc-8 generates more precise line info, making
the instruction at 0x4004b9 a "recommended breakpoint location", such that gdb
no longer prints the instruction address.

Fix this by getting the instruction address by printing $pc.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-05-06  Tom de Vries  <tdevries@suse.de>

	* gdb.base/watchpoint-reuse-slot.exp (stepi): Print $pc to get current
	address.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-05-06  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.base/watchpoint-reuse-slot.exp (stepi): Print $pc to get current
+	address.
+
 2020-05-06  Tom de Vries  <tdevries@suse.de>
 
 	* gdb.base/watchpoint-reuse-slot.exp: Fix incorrect assignment.

gdb/testsuite/gdb.base/watchpoint-reuse-slot.exp

@@ -66,8 +66,8 @@ proc stepi {} {
     set srcline "  for (i = 0; i < 100000; i++); /* stepi line */"
     set test "stepi advanced"
     gdb_test_multiple "stepi" $test {
-	-re "($hex).*[string_to_regexp $srcline]\r\n$gdb_prompt $" {
-	    set addr $expect_out(1,string)
+	-re -wrap "[string_to_regexp $srcline]" {
+	    set addr [get_valueof "/x" "\$pc" "0"]
 	    if {$addr != $cur_addr} {
 		pass $test
 	    } else {