Remove throw spec from omp.h for clang

[larroy]

This fixes compilation with OMP using the Clang compiler.

[chyunsu3]

I suspect the memory error is due to race condition

[larroy]

@hcho3 in CI ?

[chyunsu3]

@larroy Yes, the memory error you can see in Travis CI is intermittent

[larroy]

#560

[larroy]

#559

[larroy]

@hcho3 can we merge this? I need it for an MXNet PR.

[chyunsu3]

Merging this for now. I'll create a new issue about failing tests for dmlc_exception and std_exception.

[larroy]

seems it's not failing due to double free anymore.

[leezu]

@larroy should this be #if defined(__ANDROID__) || defined (__clang__) instead of #if defined(__ANDROID__) && defined (__clang__). The second doesn't make much sense to me and in fact doesn't work with clang

[larroy]

I think the intention was to fix it for Android only, when using clang, hence &&, don't remember the details. But see that we are compiling with Clang in CI for a while, why did it start failing now?