glsl: Add ir_unop_sin_reduced and ir_unop_cos_reduced

The operate just like ir_unop_sin and ir_unop_cos except that they
expect their inputs to be limited to the range [-pi, pi].  Several
GPUs require this limited range for their sine and cosine
instructions, so having these as operations (along with a to-be-written
lowering pass) helps this architectures.

These new operations also matche the semantics of the
GL_ARB_fragment_program SCS instruction.  Having these as operations
helps in generating GLSL IR directly from assembly fragment programs.

src/glsl/ir.cpp

@@ -239,6 +239,8 @@ static const char *const operator_strs[] = {
    "round_even",
    "sin",
    "cos",
+   "sin_reduced",
+   "cos_reduced",
    "dFdx",
    "dFdy",
    "noise",