The Go compiler and linker are currently built as command line tools. This issue proposes refactoring so they can be used as libraries.

Benefits:

• External applications could compile code in a server (or even browser) environment. For example a wasm mode for https://compile.jsgo.io/ and https://play.jsgo.io/. Currently this is impossible.
• The go command line tool currently uses os/exec to spawn sub processes when it needs to compile and link. If the compiler and linker were built as libraries, this could be accomplished in-process, without the overhead of os/exec.

Problems:

• The current code directly accesses the filesystem with the os package for reading the input code and writing the output binaries. A solution would need an abstraction layer, similar to build.Config.
• The current codebase makes extensive use of package level variables to store state - this would need to be refactored.
• This will increase the public surface area of the compiler API.