${S}/src/src.pro adds -g3 and -O{0,2} to CXXFLAGS. BTW, -g3 is known to cause problems for certain applications. This problem might also be present in 1.5.x versions, but I didn't check.
Created attachment 140410 [details, diff] qgit-2.1.ebuild.patch Patch to fix the issue.
Markus, I think this one is yours. - ferdy
Fix applied in CVS, though use src_unpack for such stuff, see the new ebuild on details ;)