The purpose of this is:
* Only one way to do things
* Changing a function with void return type to return a possible
error becomes a 1 character change, subtly encouraging
people to use errors.
See #632
Here are some imperfect sed commands for performing this update:
remove arrow:
```
sed -i 's/\(\bfn\b.*\)-> /\1/g' $(find . -name "*.zig")
```
add void:
```
sed -i 's/\(\bfn\b.*\))\s*{/\1) void {/g' $(find ../ -name "*.zig")
```
Some cleanup may be necessary, but this should do the bulk of the work.
the optimizer was deleting compiler_rt symbols, so I changed
the linkage type from LinkOnce to Weak
also changed LinkOnce to mean linkonce_odr in llvm and
Weak to mean weak_odr in llvm.
See #563
* try some macos travis stuff
* put c in the link libs for macos since we always link with libSystem
* for non-native targets on macos, allow runtime symbol resolution
- it's causing an infinite loop in LLD.
* for macos, always build compiler_rt and turn on LinkOnce because
compiler_rt on darwin is missing some stuff.
