all: run gofmt on all source code

Some source code wasn't part of `FMT_PATHS` so wasn't checked for
correct formatting. This change includes all this source code and
excludes cgo/testdata because it contains files that can't be parsed.

src/crypto/rand/rand_arc4random.go

@@ -1,3 +1,4 @@
+//go:build darwin || tinygo.wasm
 // +build darwin tinygo.wasm
 
 // This implementation of crypto/rand uses the arc4random_buf function

src/crypto/rand/rand_urandom.go

@@ -1,3 +1,4 @@
+//go:build linux && !baremetal && !wasi
 // +build linux,!baremetal,!wasi
 
 // This implementation of crypto/rand uses the /dev/urandom pseudo-file to