refactor: default leancArgs to -03, -DNDEBUG (like leanpkg)

Lake/Package.lean

@@ -172,8 +172,9 @@ structure PackageConfig where
   /--
     Additional arguments to pass to `leanc`
     while compiling the C source files generated by `lean`.
+    Defaults to `-03` and `-DNDEBUG`.
   -/
-  leancArgs : Array String := #[]
+  leancArgs : Array String := #["-O3", "-DNDEBUG"]
 
   /--
     The build subdirectory to which Lake should output

README.md

@@ -82,7 +82,7 @@ Lake provides a large assortment of configuration options for packages.
 
 ### Library / Binary Compilation
 
-* `leancArgs`: An `Array` additional arguments to pass to `leanc` while compiling the C source files generated by `lean`.
+* `leancArgs`: An `Array` additional arguments to pass to `leanc` while compiling the C source files generated by `lean`. Defaults to `-03` and `-DNDEBUG`.
 * `irDir`: The build subdirectory to which Lake should output the package's intermediary results (e.g., `.c` and `.o` files). Defaults to `ir`.
 * `libName`: The name of the package's static library. Defaults to the string representation of the package's `moduleRoot`.
 * `libDir`: The build subdirectory to which Lake should output the package's static library. Defaults to `lib`.

examples/bootstrap/package.lean

@@ -5,7 +5,6 @@ package where
   name := "lake"
   srcDir := FilePath.mk ".." / ".."
   oleanDir := "."
-  leancArgs := #["-O3", "-DNDEBUG"]
   binRoot := `Lake.Main
   linkArgs :=
     if Platform.isWindows then