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