glsl linker: compare interface blocks during intrastage linking

glsl linker: compare interface blocks during intrastage linking

Verify that interface blocks match when combining compilation
units at the same stage. (For example, when merging all vertex
shaders.)

Fixes piglit glsl-1.50 test:
* linker/interface-blocks-multiple-vs-member-count-mismatch.shader_test

v5 (Ken): Rename to link_interface_blocks.cpp and drop the separate .h
file for consistency with other linker code.  Remove "ok" variable.
Fold cross_validate_interface_blocks into its caller.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>