misc/cgo/testshared: fix tests in module mode

Updates #30228

Change-Id: I5cc739eb9fdfb648ec45e350d43d4cb02e450553
Reviewed-on: https://go-review.googlesource.com/c/163211
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

misc/cgo/testshared/testdata/implicitcmd/implicitcmd.go

@@ -0,0 +1,10 @@
+package main
+
+import (
+	"testshared/explicit"
+	"testshared/implicit"
+)
+
+func main() {
+	println(implicit.I() + explicit.E())
+}