Add support of Zephyr OS

[anobli]

This updates googletest in order to use it with Zephyr.
The first patch update gtest itself to support Zephyr OS it self.
The second adds files used by Zephyr build system. If this is not acceptable, then I will drop it and find another way to integrate it to zephyr build system.

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[dkaszews]

What little I can review and understand looks good to me

[jeffwelder-ellenbytech]

+1

This is fantastic, and works great out of the box.
Attached is how I pulled it into my zephyr project.

manifest:
  remotes:
    - name: zephyrproject-rtos
      url-base: https://github.com/zephyrproject-rtos
    - name: anobli
      url-base: https://github.com/anobli

  projects:
    - name: googletest
      remote: anobli
      repo-path: googletest
      revision: 8e3886acac2e6058f4f540269f43b1f4a2700adc
    - name: zephyr
      remote: zephyrproject-rtos
      revision: v4.1.0
      import:
        name-blocklist:
          - hal_altera
          - hal_cypress
          - hal_infineon
          - hal_microchip
          - hal_nxp
          - hal_openisa
          - hal_silabs
          - hal_xtensa
          - hal_ti
          - loramac-node
          - ci-tools
          - edtt
          - sof
          - matter
  self:
    path: application