Include python headers even if nested. (#2669)

* Some python versions/installations use trampoline headers at the root.
diff --git a/bindings/python/build_tools/python/generate_build.py b/bindings/python/build_tools/python/generate_build.py
index 6d8cff4..6705cfd 100644
--- a/bindings/python/build_tools/python/generate_build.py
+++ b/bindings/python/build_tools/python/generate_build.py
@@ -64,7 +64,7 @@
 
 cc_library(
     name = "python_headers",
-    hdrs = glob(["include/*.h"]),
+    hdrs = glob(["include/**/*.h"]),
     srcs = [{extra_srcs}],
     includes = ["include"],
     linkopts = [],