Replace CMAKE_SOURCE_DIR with PROJECT_SOURCE_DIR

Change-Id: Ib4889cbe67b6b2b5434ad36814f872bf2912ec45
Bug: dawn:1974
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/146740
Reviewed-by: Ben Clayton <[email protected]>
Kokoro: Kokoro <[email protected]>
Commit-Queue: Ben Clayton <[email protected]>
Reviewed-by: Austin Eng <[email protected]>

Author: sparist

src/dawn/node/CMakeLists.txt

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 set(DAWN_NODE_GEN_DIR "${DAWN_BUILD_GEN_DIR}/node")
-set(IDLGEN_TOOL_DIR   "${CMAKE_SOURCE_DIR}/tools/src/cmd/idlgen")
+set(IDLGEN_TOOL_DIR   "${PROJECT_SOURCE_DIR}/tools/src/cmd/idlgen")
 
 # idlgen() is a function that uses the tools/src/cmd/idlgen/main.go tool to
 # generate code from an IDL file and template.