gdb/testsuite: allowed for function_range to deal with mangled functions

When calling get_func_info inside a test case, it would cause failures
if the function was printed using a C++ style mangled name. The current
patch fixes this by allowing for mangled names along with the current
rules.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/testsuite/lib/dwarf.exp

@@ -400,7 +400,7 @@ proc function_range { func src {options {debug}} } {
     if { $func_length != 0 } {
 	set func_pattern "$func_pattern\\+$func_length"
     }
-    set test "x/2i $func+$func_length"
+    set test "with print asm-demangle on -- x/2i $func+$func_length"
     gdb_test_multiple $test $test {
 	-re ".*($hex) <$func_pattern>:\[^\r\n\]+\r\n\[ \]+($hex).*\.\r\n$gdb_prompt $" {
 	    set start $expect_out(1,string)