Rollup merge of rust-lang#42055 - michaelwoerister:reenable-incremental-cc, r=nikomatsakis

Enable cross-crate incremental compilation by default.

Now that direct metadata hashing has been implemented for a while and we haven't seen any problems with it over at [rust-icci](https://travis-ci.org/rust-icci/), let's re-enable cross crate support for incremental compilation again.

r? @nikomatsakis

Author: Mark-Simulacrum

src/librustc/session/config.rs

@@ -963,7 +963,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "attempt to recover from parse errors (experimental)"),
     incremental: Option<String> = (None, parse_opt_string, [UNTRACKED],
           "enable incremental compilation (experimental)"),
-    incremental_cc: bool = (false, parse_bool, [UNTRACKED],
+    incremental_cc: bool = (true, parse_bool, [UNTRACKED],
           "enable cross-crate incremental compilation (even more experimental)"),
     incremental_info: bool = (false, parse_bool, [UNTRACKED],
         "print high-level information about incremental reuse (or the lack thereof)"),

src/test/incremental/add_private_fn_at_krate_root_cc/auxiliary/point.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 pub struct Point {
     pub x: f32,
     pub y: f32,

src/test/incremental/callee_caller_cross_crate/auxiliary/a.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 #![crate_type="rlib"]
 
 #[cfg(rpass1)]

src/test/incremental/change_private_fn_cc/auxiliary/point.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 pub struct Point {
     pub x: f32,
     pub y: f32,

src/test/incremental/change_private_impl_method_cc/auxiliary/point.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 pub struct Point {
     pub x: f32,
     pub y: f32,

src/test/incremental/remapped_paths_cc/auxiliary/extern_crate.rs

@@ -10,7 +10,6 @@
 
 // ignore-tidy-linelength
 
-// aux-build:extern_crate.rs
 //[rpass1] compile-flags: -g
 //[rpass2] compile-flags: -g
 //[rpass3] compile-flags: -g -Zremap-path-prefix-from={{src-base}} -Zremap-path-prefix-to=/the/src

src/test/incremental/remove-private-item-cross-crate/auxiliary/a.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 #![allow(warnings)]
 #![crate_name = "a"]
 #![crate_type = "rlib"]

src/test/incremental/rlib_cross_crate/auxiliary/a.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
 // no-prefer-dynamic
 
 #![crate_type="rlib"]

src/test/incremental/struct_change_field_type_cross_crate/auxiliary/a.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 #![crate_type="rlib"]
 
  #[cfg(rpass1)]

src/test/incremental/type_alias_cross_crate/auxiliary/a.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z incremental-cc
-
 #![crate_type="rlib"]
 
 #[cfg(rpass1)]