Use MACRO_AT_func in entry-values.exp

Use MACRO_AT_func in entry-values.exp

MACRO_AT_func can be used in gdb.trace/entry-values.exp to correctly
get function's address in generated debug info.  As a result, the test
is more friendly to clang.  Currently, there are some fails in
entry-values.exp when the test is compiled by clang.  With this patch
applied, all fails go away.

gdb/testsuite:

2014-11-22  Yao Qi  <yao@codesourcery.com>

	* gdb.trace/entry-values.c: Remove asms.
	(foo): Add foo_label.
	(bar): Add bar_label.
	* gdb.trace/entry-values.exp: Remove code computing  foo's
	length and bar's length.
	(Dwarf::assemble): Invoke function_range for bar and use
	MACRO_AT_func for foo.