[gdb/testsuite] Fix -readnow FAIL in gdb.base/style.exp

When running test-case gdb.base/style.exp with target board readnow, we run
into:
...
FAIL: gdb.base/style.exp: filename is styled when loading symbol file
...

The problem is that with -readnow, an extra "Expanding full symbols" message
is generated:
...
(gdb) file $file^M
Reading symbols from $file...^M
Expanding full symbols from $file...^M
(gdb) FAIL: gdb.base/style.exp: filename is styled when loading symbol file
...
and the test does not expect this message.

Fix this by expecting the additional message for -readnow.

gdb/testsuite/ChangeLog:

2020-04-10  Tom de Vries  <tdevries@suse.de>

	* gdb.base/style.exp: Expect "Expanding full symbols" message for
	-readnow.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-04-10  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.base/style.exp: Expect "Expanding full symbols" message for
+	-readnow.
+
 2020-04-10  Tom de Vries  <tdevries@suse.de>
 
 	PR cli/25808

gdb/testsuite/gdb.base/style.exp

@@ -34,6 +34,8 @@ save_vars { env(TERM) } {
 	return -1
     }
 
+    set readnow [readnow]
+
     if {![runto_main]} {
 	fail "style tests failed"
 	return
@@ -140,8 +142,15 @@ save_vars { env(TERM) } {
 	    ]
 
     set quoted [string_to_regexp $binfile]
+    set pass_re "Reading symbols from [style $quoted file]\.\.\."
+    if { $readnow } {
+	set pass_re \
+	    [multi_line \
+		 $pass_re \
+		 "Expanding full symbols from [style $quoted file]\.\.\."]
+    }
     gdb_test "file $binfile" \
-	"Reading symbols from [style $quoted file]..." \
+	$pass_re \
 	"filename is styled when loading symbol file"
 
     gdb_test "pwd" "Working directory [style .*? file].*"