Does not compile with Clang

[eholum]

Relevant for IKOS.

The cobra package's makefile has unsupported arguments for clang compilers, which causes build errors,

make[3]: warning: jobserver unavailable: using -j1.  Add '+' to parent make rule.
error: unknown warning option '-Wformat-truncation=1' [-Werror,-Wunknown-warning-option]
make[3]: *** [<builtin>: cobra_prim.o] Error 1
gmake[2]: *** [CMakeFiles/cobra-4.8.dir/build.make:86: cobra-4.8/src/cobra-4.8-stamp/cobra-4.8-build] Error 2
gmake[1]: *** [CMakeFiles/Makefile2:137: CMakeFiles/cobra-4.8.dir/all] Error 2
gmake: *** [Makefile:134: all] Error 2
--- stderr: cobra_vendor                             
Cloning into 'cobra-4.8'...
HEAD is now at 5af7230 Add files via upload
make[3]: warning: jobserver unavailable: using -j1.  Add '+' to parent make rule.
error: unknown warning option '-Wformat-truncation=1' [-Werror,-Wunknown-warning-option]
make[3]: *** [<builtin>: cobra_prim.o] Error 1
gmake[2]: *** [CMakeFiles/cobra-4.8.dir/build.make:86: cobra-4.8/src/cobra-4.8-stamp/cobra-4.8-build] Error 2
gmake[1]: *** [CMakeFiles/Makefile2:137: CMakeFiles/cobra-4.8.dir/all] Error 2
gmake: *** [Makefile:134: all] Error 2
---
Failed   <<< cobra_vendor [3.25s, exited with code 2]

This prevents the ikos scanning tool from running on the package.

[eholum]

I pushed a rather ugly fix for this here, eholum@6a8d6d6, which modifies the cobra makefile prior to building if we're using clang.

[asymingt]

@Bckempa can you take a look at this one, because I think it's related to SpaceROS?