This update for gn, re2 fixes the following issues:

Changes in gn:

- Bump Leap's GCC version to 12 to align with the other Chromium
  tools
- Exclude ppc - it doesn't build

Changes in re2:

- Require GCC 12 on Leap due to code containing speed ups which
  require newer standards
- Allow tests to fail - they fail too often

- update to 2023-03-01:

  * changes for other platforms

- update to 2023-02-01:

  * improved support for ICU

- build with ICU

- update to 2022-12-01:

  * Update to Unicode 15.0.0 data 
  * cmake install now installs the pkg-config file

- update to 2022-06-01:

  * switch to cxx_std_11 and other developer visible fixes