glsl/nir: Use nir_builder's new control-flow helpers
glsl/nir: Use nir_builder's new control-flow helpers

Reviewed-by: Samuel Iglesias Gonsálvez <b753b212f30aed827c3eea2e437609dc37310153@igalia.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler