compiler: add the --compiler-path option

src/julec/compile.jule

@@ -227,9 +227,13 @@ fn check_compiler_flag() {
     | "":
         throw("missing option value: --compiler")
     | "clang":
-        env::COMPILER_PATH = "clang++"
+        if env::COMPILER_PATH == "" {
+            env::COMPILER_PATH = "clang++"
+        }
     | "gcc":
-        env::COMPILER_PATH = "g++"
+        if env::COMPILER_PATH == "" {
+            env::COMPILER_PATH = "g++"
+        }
     |:
         throw("invalid option value for --compiler: " + env::COMPILER)
     }
@@ -311,6 +315,7 @@ fn check_flags(&args: []str): []str {
     fs.add_var[bool](unsafe { (&bool)(&env::SHADOWING) }, "shadowing", 0, "Allow shadowing")
     fs.add_var[bool](unsafe { (&bool)(&env::TRANSPILATION) }, "transpile", 't', "Transpile code")
     fs.add_var[str](unsafe { (&str)(&env::COMPILER) }, "compiler", 0, "Backend compiler")
+    fs.add_var[str](unsafe { (&str)(&env::COMPILER_PATH) }, "compiler-path", 0, "Path of backend compiler")
     fs.add_var[bool](unsafe { (&bool)(&env::PRODUCTION) }, "production", 'p', "Compile for production")
     fs.add_var[bool](unsafe { (&bool)(&env::RC) }, "disable-rc", 0, "Disable reference counting")
     fs.add_var[bool](unsafe { (&bool)(&env::SAFETY) }, "disable-safety", 0, "Disable safety")

src/julec/init.jule

@@ -8,6 +8,6 @@ use env
 // These codes should be executed on all platforms.
 fn __init_common() {
     // Configure compiler to default by platform
+    // Compiler path will be set by compiler before compilation if still unassigned.
     env::COMPILER = "clang"
-    env::COMPILER_PATH = "clang++"
 }