Define NODE_JS_EXECUTABLE based on an env var (#190)

* Define NODE_JS_EXECUTABLE based on an env var

This is necessary for halide/Halide#6356 to land -- if we are building/testing wasm, we need to set NODE_JS_EXECUTABLE properly; this patch does so based on an env var ('HALIDE_NODE_JS_PATH') which is assumed to be defined on the relevant wokers.

* Update master.cfg

master/master.cfg

@@ -587,6 +587,11 @@ def get_halide_cmake_definitions(builder_type, halide_target='host'):
     if builder_type.os == 'windows':
         cmake_definitions['CMAKE_TOOLCHAIN_FILE'] = Interpolate('%(prop:VCPKG_ROOT)s/scripts/buildsystems/vcpkg.cmake')
 
+    # TODO: HALIDE_NODE_JS_PATH is only necessary until EMSDK updates their built-in version of Node
+    # to v16.13+; when that is done, remove this definition.
+    if builder_type.handles_wasm():
+        cmake_definitions['NODE_JS_EXECUTABLE'] = Property('HALIDE_NODE_JS_PATH')
+
     return cmake_definitions
 
 
@@ -703,8 +708,13 @@ def add_env_setup_step(factory, builder_type, enable_ccache=False):
         'LD': ld,
     }
 
+    # TODO: HALIDE_NODE_JS_PATH is only necessary until EMSDK updates their built-in version of Node
+    # to v16.13+; when that is done, remove HALIDE_NODE_JS_PATH here and on the workers.
     factory.addStep(SetPropertiesFromEnv(name='Read worker environment',
-                                         variables=['VCPKG_ROOT', 'LD_LIBRARY_PATH', 'HL_HEXAGON_TOOLS']))
+                                         variables=['VCPKG_ROOT',
+                                                    'LD_LIBRARY_PATH',
+                                                    'HL_HEXAGON_TOOLS',
+                                                    'HALIDE_NODE_JS_PATH']))
 
     vcpkg_root = Property('VCPKG_ROOT', default=None)