This makes CGo-emitted diagnostics very similar to regular errors
emitted while parsing/typechecking a package.
It's not complete, but after introducing some errors in testdata/cgo,
this is the resulting output:
# ./testdata/cgo/
testdata/cgo/main.h:18:11: error: a parameter list without types is only allowed in a function definition
testdata/cgo/main.go:5:10: note: in file included from testdata/cgo/main.go!cgo.c:2:
testdata/cgo/main.go:6:19: error: expected identifier or '('
Previously, this was the output:
/home/ayke/src/github.com/tinygo-org/tinygo/testdata/cgo/main.h:18:11: error: a parameter list without types is only allowed in a function definition
cgo-fake.c:3:19: error: expected identifier or '('
# ./testdata/cgo/
cgo: libclang cannot parse fragment
So far, we've pretended to be js/wasm in baremetal targets to make the
stdlib happy. Unfortunately, this has various problems because
syscall/js (a dependency of many stdlib packages) thinks it can do JS
calls, and emulating them gets quite hard with all changes to the
syscall/js packages in Go 1.12.
This commit does a few things:
* It lets baremetal targets pretend to be linux/arm instead of
js/wasm.
* It lets the loader only select particular packages from the src
overlay, instead of inserting them just before GOROOT. This makes it
possible to pick which packages to overlay for a given target.
* It adds a baremetal-only syscall package that stubs out almost all
syscalls.
