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/repl/repl_test.v

@@ -0,0 +1,40 @@
+import os
+import compiler.tests.repl.runner
+import benchmark
+
+fn test_the_v_compiler_can_be_invoked() {
+	vexec := runner.full_path_to_v()
+	println('vexecutable: $vexec')
+	assert vexec != ''
+
+	vcmd := '$vexec --version'
+	r := os.exec(vcmd) or { panic(err) }
+	//println('"$vcmd" exit_code: $r.exit_code | output: $r.output')
+	assert r.exit_code == 0
+
+	vcmd_error := '$vexec nonexisting.v'
+	r_error := os.exec(vcmd_error) or { panic(err) }
+	//println('"$vcmd_error" exit_code: $r_error.exit_code | output: $r_error.output')
+	assert r_error.exit_code == 1
+	assert r_error.output == '`nonexisting.v` does not exist'
+}
+
+fn test_all_v_repl_files() {
+	options := runner.new_options()
+	mut bmark := benchmark.new_benchmark()
+	for file in options.files {
+		bmark.step()
+		fres := runner.run_repl_file(options.wd, options.vexec, file) or {
+			bmark.fail()
+			eprintln( bmark.step_message(err) )
+			assert false
+			continue
+		}
+		bmark.ok()
+		println( bmark.step_message(fres) )
+		assert true
+	}
+	bmark.stop()
+	println( bmark.total_message('total time spent running REPL files') )
+}
+