Disable debuginfo when compiling tools

Currently the Cargo binary has jumped from 14M to 34M on the beta channel, which
appears to be due to the fact that we're compiling tools with debug information
inside them. This additionally means that the `rls` binary is 62M right now!

This wasn't an intentional change, so be sure to disable debuginfo when
compiling tools as it's just intended for the standard library and compile for
now.

src/bootstrap/lib.rs

@@ -464,8 +464,6 @@ impl Build {
              .env("RUSTC", self.out.join("bootstrap/debug/rustc"))
              .env("RUSTC_REAL", self.compiler_path(compiler))
              .env("RUSTC_STAGE", stage.to_string())
-             .env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string())
-             .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string())
              .env("RUSTC_CODEGEN_UNITS",
                   self.config.rust_codegen_units.to_string())
              .env("RUSTC_DEBUG_ASSERTIONS",
@@ -477,6 +475,13 @@ impl Build {
              .env("RUSTDOC_REAL", self.rustdoc(compiler))
              .env("RUSTC_FLAGS", self.rustc_flags(target).join(" "));
 
+        // Tools don't get debuginfo right now, e.g. cargo and rls don't get
+        // compiled with debuginfo.
+        if mode != Mode::Tool {
+             cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string())
+                  .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string());
+        }
+
         // Enable usage of unstable features
         cargo.env("RUSTC_BOOTSTRAP", "1");
         self.add_rust_test_threads(&mut cargo);