Legion: add redop_half variant, and add missing build dependency (#44792)

* legion: add redop_half variant
* legion: conditionally add py-setuptools as build dependency
   Dependency exists only for '+python' variant.

var/spack/repos/builtin/packages/legion/package.py

@@ -121,6 +121,7 @@ def patch(self):
     depends_on("py-cffi", when="+python")
     depends_on("py-numpy", when="+python")
     depends_on("py-pip", when="+python", type="build")
+    depends_on("py-setuptools", when="+python", type="build")
 
     depends_on("papi", when="+papi")
     depends_on("zlib-api", when="+zlib")
@@ -267,6 +268,12 @@ def validate_gasnet_root(value):
     variant(
         "redop_complex", default=False, description="Use reduction operators for complex types."
     )
+    requires("+redop_complex", when="+bindings")
+    variant(
+        "redop_half",
+        default=False,
+        description="Use reduction operators for half precision types.",
+    )
 
     variant(
         "max_dims",
@@ -415,10 +422,14 @@ def cmake_args(self):
             # default is off.
             options.append("-DLegion_BUILD_BINDINGS=ON")
 
-        if spec.satisfies("+redop_complex") or spec.satisfies("+bindings"):
+        if spec.satisfies("+redop_complex"):
-            # default is off; required for bindings.
+            # default is off
             options.append("-DLegion_REDOP_COMPLEX=ON")
 
+        if spec.satisfies("+redop_half"):
+            # default is off
+            options.append("-DLegion_REDOP_HALF=ON")
+
         maxdims = int(spec.variants["max_dims"].value)
         # TODO: sanity check if maxdims < 0 || > 9???
         options.append("-DLegion_MAX_DIM=%d" % maxdims)