Comment # 1 on bug 1058444 from Richard Biener

I assume you are building for x86_64.

> iobs api /build/SUSE:SLE-11-SP4:Update/standard/x86_64/_repository | grep gcc5
  <binary filename="gcc5.rpm" size="14423494" mtime="1497444028" />
  <binary filename="gcc5-32bit.rpm" size="5408198" mtime="1497444020" />
  <binary filename="gcc5-ada.rpm" size="19879094" mtime="1497444030" />
  <binary filename="gcc5-ada-32bit.rpm" size="5999244" mtime="1497444028" />
  <binary filename="gcc5-c++.rpm" size="6745131" mtime="1497444031" />
  <binary filename="gcc5-c++-32bit.rpm" size="11332" mtime="1497444030" />
...

so it is there.  You need to build against SUSE:SLE-11-SP4:Update, the package
isn't in :GA.