GCC 4.5.0 as a default compiler for mozilla-central linux and linux64 platforms

[Rail Aliev]

The RelEng Team plans to switch to GCC 4.5.0 and use it as a default
compiler for mozilla-central linux and linux64 builds. GCC 4.5.0 allows
us to produce profiled builds for Linux. See Bug 559964 [1] for the details.

We plan to deploy GCC 4.5.0 today, June 8, which means it should be
available on slaves approximately within 24 hours, so developers can set
CC to /tools/gcc-4.5/bin/gcc and CXX to /tools/gcc-4.5/bin/g++ in their
try builds starting tomorrow.

Due to lack of time for testing GCC 4.5.0 based builds the RelEng Team
decided to switch to GCC 4.5.0 for nightly and on-checkin builds after
3.7a5, which build should be started tomorrow, June 9.

After successful testing of GCC 4.5.0 as a default compiler for
mozilla-central nightly and on-checkin builds, we plan to enable it as a
default compiler for mozilla-central based branches (addonsmgr,
electrolysis, places and tracemonkey), and enable PGO for linux and
linux64 builds within 1 week.

Please let me know if you have any reason why we should not proceed with
this plan.

1. https://bugzilla.mozilla.org/show_bug.cgi?id=559964

--
Best,
Rail Aliev