R: fixes for gcc build and CLT > 6.0.

- Disable building against Aqua with Xcode/CLT 6.1
- patch for gcc to build correctly against Accelerate.

Fixes #1304.
Closes #1533.
r: update 3.1.2_1 bottle.
fasttree 2.1.7: Use OpenMP
fasttree: add 2.1.7 bottle.