[arm] Fix fails in dw2-compdir-oldgcc.exp

This patch fixes two fails in dw2-compdir-oldgcc.exp I've seen on arm
target thumb mode.

  FAIL: gdb.dwarf2/dw2-compdir-oldgcc.exp: info source gcc42
  FAIL: gdb.dwarf2/dw2-compdir-oldgcc.exp: info source gcc43

When fill in DW_AT_low_pc, the label should be used rather than the
function, otherwise, the LSB bit of the address in DW_AT_low_pc is
set and the debug info is wrong.  This patch is to add two labels for
functions gcc42 and gcc43 respectively, and use them.  These two
fails are fixed.

gdb/testsuite:

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

	* gdb.dwarf2/dw2-compdir-oldgcc.S: Define label .Lgcc42_procstart
	and .Lgcc43_procstart.  Use .Lgcc42_procstart instead of gcc42.
	Use .Lgcc43_procstart instead of gcc43.
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.
Check branch displacement overflow in x86-64 PLT entry

Displacement of branch to PLT0 in x86-64 PLT entry is signed 32-bit.
This patch adds a sanity check.  We will only see the failure when PLT
size is > 2GB.

	* elf64-x86-64.c (elf_x86_64_finish_dynamic_symbol): Check
	branch displacement overflow in PLT entry.
cp-namespace.c (cp_lookup_symbol_nonlocal): Fix comment.

gdb/ChangeLog:

	* cp-namespace.c (cp_lookup_symbol_nonlocal): Fix comment.
symtab.c: Comment and whitespace improvements.

gdb/ChangeLog:

	* symtab.c (lookup_symbol_in_objfile_from_linkage_name): Improve
	function comment.
	(search_symbols): Fix comments and whitespace.
Automatic date update in version.in