Normalize Python_SITEARCH before passing to find_package

vcpkg overrides find_package with a macro that stores \${ARGN} in a
double-quoted string.  Textual macro substitution causes the value to
be re-parsed as a string literal, so a Windows path whose components
start with a letter (e.g. \build_bot -> \b) triggers CMake's CMP0010
invalid-escape-sequence error.  Normalizing with file(TO_CMAKE_PATH)
converts backslashes to forward slashes before the path reaches the
macro.

No upstream vcpkg issue exists for this as of 2026-02-25.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: alexreinking

apps/onnx/CMakeLists.txt

@@ -108,6 +108,13 @@ if (NOT Python_FOUND)
     return()
 endif ()
 
+# Normalize to forward slashes before passing to find_package. vcpkg overrides
+# find_package with a macro that stores ${ARGN} in a double-quoted string; if
+# the path contains a backslash followed by a letter (e.g. \build_bot -> \b),
+# CMake treats it as an escape sequence and errors (CMP0010). file(TO_CMAKE_PATH)
+# converts native separators to forward slashes, sidestepping the issue on all
+# CMake versions.
+file(TO_CMAKE_PATH "${Python_SITEARCH}" Python_SITEARCH)
 find_package(pybind11 HINTS "${Python_SITEARCH}")
 if (NOT pybind11_FOUND)
     message(WARNING "Could NOT find pybind11")