C compiler (typically gcc or clang) cannot be found on the system PATH.
You can override the default by setting the CGO_ENABLED
environment variable when running the go tool: set it to 1 to enable
the use of cgo, and to 0 to disable it. The go tool will set the
build constraint "cgo" if cgo is enabled. The special import "C"
implies the "cgo" build constraint, as though the file also said
"//go:build cgo".  Therefore, if cgo is disabled, files that import

		c = append(c,
			"-ferror-limit=0",
			// Apple clang version 1.7 (tags/Apple/clang-77) (based on LLVM 2.9svn)
			// doesn't have -Wno-unneeded-internal-declaration, so we need yet another
			// flag to disable the warning. Yes, really good diagnostics, clang.
			"-Wno-unknown-warning-option",
			"-Wno-unneeded-internal-declaration",
			"-Wno-unused-function",
			"-Qunused-arguments",

// pointer types, because we generate code passing a struct ptr rather
// than using the typedef. This warning is expected and does not break
// a normal build.
// We can only disable -Wincompatible-pointer-types starting with GCC 5.

// #if __GNU_MAJOR__ >= 5
//
// #pragma GCC diagnostic ignored "-Wincompatible-pointer-types"
//
// typedef struct {
// 	int a;

		return f, nil
	}

	f, err := parser.ParseFile(fset, filename, nil, parser.ParseComments)
	if err != nil {
		return nil, err
	}
	parsedFileCache[filename] = f

	return f, nil
}

// Disable before debugging non-obvious errors from the type-checker.
const usePkgCache = true

var (
	pkgCache = map[string]*apiPackage{} // map tagKey to package