Fix Travis, which has problems with BB

[staticfloat]

Disable libunwind and libuv because they were built with ld version 2.26 and linking against static libraries with an older ld is apparently not as compatible as we would like.

[staticfloat]

As best I can tell, the i686 Travis failure (complaining about undefined reference to '__stack_chk_fail') might be fixed by manually including -lssp? I'm not sure, just reading off of Stack Overflow. I'm confused because we have -fstack-protector-all already being sent to the compiler, so I would think that -lssp would be unnecessary.

[vchuravy]

We set

julia/sysimage.mk

Line 18 in 0557467

$$([ $(OS) = WINNT ] && echo '' -lssp))

and

julia/Make.inc

Line 1126 in e49a7c7

OSLIBS += -lssp

here.

[staticfloat]

Thanks Valentin, that's really helpful.

[staticfloat]

This is a little conservative, (disabling BB-built LLVM wholesale) but I think it's worth it to fix it now and then iterate on it later if need be.