* Use set -ex
* Use -std=c++14 so -latomic can be found

* Use set -ex
* Use -std=c++14 so -latomic can be found

This configuration builds both 32-bit and 64-bit binaries for Mac OS X.
One thing I had to change was to increase our minimum supported version
for 10.7 to 10.9, because 10.9 (Mavericks) appears to be the earliest
version supporting C++11.