[SR-8866] build-script should default to LLVM_USE_LINKER=gold if gold is available

[kevints]

Previous ID	SR-8866
Radar	None
Original Reporter	@kevints
Type	Improvement

Additional Detail from JIRA

Votes	0
Component/s	Project Infrastructure
Labels	Improvement, CMake
Assignee	None
Priority	Medium

md5: a656328a25495a95d8efbd9ff685edc7

Issue Description:

On Ubuntu 14.04 a clean build of swift from a fresh clone takes a long time with the default flags to build-script. Much of this can be attributed to the use of the GNU ld linker. Right now you can get a great speed increase by passing --extra-cmake-options=-DLLVM_USE_LINKER=gold to build-script. Is there any reason not to make this the default?

[belkadan]

We do this already for the Swift build, but I guess we should do it for the LLVM build too.