program_gl_utils: do not relink the program if it is not necessary
program_gl_utils: do not relink the program if it is not necessary

Linking the GL program is an expensive operation. Skipping this
operation greatly reduces the graph initialization time when a shader is
shared across a bunch of nodes for contexts that do support explicit
bindings and locations.

gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl