Python cmake path issues on windows

[nicolemarsaglia]

Turning python=ON in windows build makes it very unhappy:

-- Found Python: C:/hostedtoolcache/windows/Python/3.7.9/x64/libs/python37.lib  
CMake Error at blt/cmake/BLTMacros.cmake:340 (cmake_parse_arguments):
  Syntax error in cmake code at

    D:/a/ascent/ascent/src/blt/cmake/BLTMacros.cmake:341

  when parsing string

    NAME;python;INCLUDES;C:\hostedtoolcache\windows\Python\3.7.9\x64\include;LIBRARIES;C:/hostedtoolcache/windows/Python/3.7.9/x64/libs/python37.lib

  Invalid character escape '\h'.
Call Stack (most recent call first):
  cmake/thirdparty/SetupPython.cmake:439 (blt_register_library)
  cmake/Setup3rdParty.cmake:18 (include)
  CMakeLists.txt:139 (include)


-- Configuring incomplete, errors occurred!