Description:

The gcc packages in Arch are built with a modified version string, which causes them to report an incorrect version. The new upstream GCC numbering scheme was intentionally designed so that we can distinguish bug reports for official releases such as 5.3.0 from pre-release snapshots such as 5.3.1 20160209. The Arch packages break this, causing users to report bugs upstream for "GCC 5.3.0" which are not actually present in GCC 5.3.0 e.g.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70735

This wastes upstream devs' time because it makes it harder to identify the version being used by Arch users and causes confusion for identifying regressions.

The culprit is this line in your build script:
https://projects.archlinux.org/svntogit/packages.git/tree/gcc/trunk/PKGBUILD#n48

That might have made sense prior to GCC 5 (although I still found it annoying that your users would say they had a bug in 4.9.3 when it was really a bug in a pre-release 4.9.4 YYYYMMDD snapshot) but the new numbering scheme introduced with GCC 5 makes this unnecessary and only causes confusion.

Steps to reproduce:

gcc -v