compiler: make compiler an ordinary vlib/compiler module

* Move compiler/ under vlib/compiler/ .

* Add a minimal compiler/main.v driver program.

* Cleanup compiler/main.v .

* Make most compiler tests pass again.

* Apply the fix by @joe-conigliaro , so that the rest of the compiler tests are fixed too.

* Thanks to @avitkauskas, now the vlib/vcompiler/tests/str_gen_test.v test does not need to be special cased anymore.

* Reapply @joe-conigliaro fix for vgen.

vlib/compiler/tests/module_test.v

@@ -0,0 +1,18 @@
+import os
+import time as t
+import crypto.sha256 as s2
+
+import (
+	math
+	log as l
+	crypto.sha512 as s5
+)
+
+fn test_import() {
+	assert os.SUCCESS == os.SUCCESS &&
+		t.month_days[0] == t.month_days[0] &&
+		s2.Size == s2.Size &&
+		math.pi == math.pi &&
+		l.INFO == l.INFO &&
+		s5.Size == s5.Size
+}