Ok, after trying to build an older Mesa version (Git:HEAD/5a4e0f3873 + patches from Mesa master to build with a recent LLVM 3.6), which I've built successfully in the past, I get the same FTBFS now.
After downgrading binutils to 2.24.51.20140818-1 (the version I've used in the successful build of Mesa 5a4e0f3873), and also downgrading gcc (+ all libraries from the gcc-4.9 package Mesa needs) to 4.9.1-12, because later gcc packages require newer binutils versions, I was able to build even the version I attempted to build yesterday (Mesa c3f17bb18f)
Ok, after trying to build an older Mesa version (Git:HEAD/ 5a4e0f3873 + patches from Mesa master to build with a recent LLVM 3.6), which I've built successfully in the past, I get the same FTBFS now.
After downgrading binutils to 2.24.51.20140818-1 (the version I've used in the successful build of Mesa 5a4e0f3873), and also downgrading gcc (+ all libraries from the gcc-4.9 package Mesa needs) to 4.9.1-12, because later gcc packages require newer binutils versions, I was able to build even the version I attempted to build yesterday (Mesa c3f17bb18f)
In no build I had LTO activated.
So it seems like this is a bug in binutils/gcc?