switch Clang from broken Ubuntu PPA to upstream binary release

[efidler]

This should fix the Travis clang builds

travis-ci/travis-ci#6120

[coveralls]

Coverage remained the same at 100.0% when pulling 0503f57 on efidler:travis-clang into e6895ec on miloyip:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 5954057 on efidler:travis-clang into e6895ec on miloyip:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 659a3e7 on efidler:travis-clang into e6895ec on miloyip:master.

[coveralls]

Coverage remained the same at 100.0% when pulling e201552 on efidler:travis-clang into e6895ec on miloyip:master.

[miloyip]

This seems not working in Travis. Any idea?

[efidler]

Yeah, it's not working yet. The current issue is that the 32-bit builds need 32-bit libc++, which isn't in the upstream binary x86_64 release of clang+llvm. What do you think of just using the clang 3.5 included in Ubuntu trusty?

[miloyip]

If clang 3.5 can compile properly, I think we can temporarily fallback to that.

[coveralls]

Coverage decreased (-0.02%) to 99.979% when pulling cad91d3 on efidler:travis-clang into 6f5e83d on miloyip:master.

[coveralls]

Coverage remained the same at 100.0% when pulling d1697f7 on efidler:travis-clang into 6f5e83d on miloyip:master.