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/fn_test.v

@@ -0,0 +1,121 @@
+// 1 line comment
+
+/* 1 line comment */
+
+/*
+multi line comment (1)
+multi line comment (2)
+multi line comment (3)
+*/
+
+/*
+	multi line comment (1)
+	/*
+		nested comment
+	*/
+	/*nested comment*/
+	/*nested comment
+*/
+	/* nested comment */
+	/* /* nested comment */ */
+	multi line comment (2)
+*/
+
+type myfn fn (int) string
+
+type myfn2 fn (a int, b int) int
+
+type myfn3 fn (int, int)
+
+fn myfn4(string)
+
+fn foobar()
+
+fn slopediv(num u32, den u32) int
+
+type f1 fn ()
+
+type f2 fn (voidptr)
+
+type f3 fn (voidptr, voidptr)
+
+type f4 fn (voidptr) int
+
+type f5 fn (int, int) int
+
+type f6 fn (int, int)
+
+fn C.atoi(byteptr) int
+
+fn foo() {
+}
+
+type actionf_v fn ()
+
+type actionf_p1 fn (voidptr)
+
+type actionf_p2 fn (voidptr, voidptr)
+
+// TODO
+fn modify_array(a mut []int) {
+	a[0] = 10
+	for i in 0..a.len {
+		a[i] = a[i] * 2
+	}
+	//a << 888
+}
+
+fn test_mut_array() {
+	mut nums := [1, 2, 3]
+	modify_array(mut nums)
+	//assert nums.len == 4
+	// println(nums)
+	assert nums[0] == 20
+	assert nums[1] == 4
+	assert nums[2] == 6
+	//assert nums[3] == 888
+	// workaround for // [91, 32, -33686272] windows bug
+	println(nums.clone())
+}
+
+fn mod_struct(user mut User) {
+	user.age++
+}
+
+struct User {
+mut:
+	age int
+}
+
+fn test_mut_struct() {
+	mut user := User{18}
+	mod_struct(mut user)
+	assert user.age == 19
+}
+
+fn mod_ptr(buf mut byteptr) {
+	buf[0] = 77
+}
+
+fn test_mut_ptr() {
+	buf := malloc(10)
+	mod_ptr(mut buf)
+	assert buf[0] == 77
+}
+
+fn high_fn(f fn(int) int) {
+
+}
+
+fn high_fn_array(f fn(a []int) []int) {
+
+}
+
+fn high_fn_multi_return(a int, b fn (c []int, d []string) ([]int, []string)) {
+
+}
+
+fn test_fns() {
+	// no asserts for now, just test function declarations above
+}
+