Qmake attempts to invoke the linker with the default `g++` binary even
when we changed the binary. This will compile error when using LTO.
For clang:
```
/usr/bin/ld.gold: error: /usr/lib/llvm-3.8/bin/../lib/LLVMgold.so: could
not load plugin library: /usr/lib/llvm-3.8/bin/../lib/LLVMgold.so:
cannot open shared object file: No such file or directory
```
For GCC:
```
lto1: fatal error: bytecode stream generated with LTO version 6.0
instead of the expected 4.1
```
Vasily
28b09e78f5