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/bench/val_vs_ptr.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int increment_val(int n) {
+	return n + 2;
+}
+
+// ~26% faster
+void increment_ptr(int* n) {
+	*n += 2;
+}
+
+int main() {
+	int n = 0;
+	for (int i = 0; i < 1000000000; i++) {
+		n = increment_val(n);
+		//increment_ptr(&n);
+	}
+	printf("%d\n", n);
+	return 0;
+}
+