Fix iree.build source directory being gitignore'd (#22391)

The gitignore path is currently wrong (it should be `iree/build`, not
`iree/compiler/build`). This switches to selectively ignoring `build`
directories instead of selectively un-ignoring, since that seems safer.

Author: rkayaith

.gitignore

@@ -22,11 +22,13 @@
 .DS_Store
 
 # CMake artifacts
-build/
-build-*/
+/build/
+/build-*/
 Testing/
-# Include iree.build package
-!compiler/bindings/python/iree/compiler/build/
+/compiler/build/
+/runtime/build/
+/integrations/tensorflow/python_projects/iree_tf/build/
+/integrations/tensorflow/python_projects/iree_tflite/build/
 
 # Bazel artifacts
 **/bazel-*