Add new plugin hooks to support querying section alignment and size.

Add new plugin hooks to support querying section alignment and size.

include/
2016-03-03  Than McIntosh <thanm@google.com>

	* plugin-api.h: Add new hooks to the plugin transfer vector to
	to support querying section alignment and section size.
	(ld_plugin_get_input_section_alignment): New hook.
	(ld_plugin_get_input_section_size): New hook.
	(ld_plugin_tag): Add LDPT_GET_INPUT_SECTION_ALIGNMENT
	and LDPT_GET_INPUT_SECTION_SIZE.
	(ld_plugin_tv): Add tv_get_input_section_alignment and
	tv_get_input_section_size.

gold/
2016-03-03  Than McIntosh  <thanm@google.com>

	* plugin.cc (Plugin::load): Include hooks for get_input_section_size
	and get_input_section_alignment in transfer vector.
	(get_input_section_alignment): New function.
	(get_input_section_size): New function.
	* testsuite/Makefile.am: Add plugin_layout_with_alignment.sh test.
	* testsuite/Makefile.in: [Regenerate.]
	* testsuite/plugin_section_alignment.cc: New test file.
	* testsuite/plugin_layout_with_alignment.cc: New test file.
	* testsuite/plugin_layout_with_alignment.sh: New test file.