glsl: Optimize the SoftFP64 shader when first creating it.

glsl: Optimize the SoftFP64 shader when first creating it.

By optimizing the shader before inlining, we avoid having to redo this
work for each inlined copy of a function.  It should also reduce the
memory consumption a bit.

This cuts the KHR-GL46.arrays_of_arrays_gl.SubroutineFunctionCalls2
runtime by 25% on my Icelake.  That test compiles many shaders, which
contain large types (dmat4) and division (expensive operations).

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>