Separate most of rustc::lint::builtin into a separate crate.

This pulls out the implementations of most built-in lints into a
separate crate, to reduce edit-compile-test iteration times with
librustc_lint and increase parallelism. This should enable lints to be
refactored, added and deleted much more easily as it slashes the
edit-compile cycle to get a minimal working compiler to test with (`make
rustc-stage1`) from

    librustc -> librustc_typeck -> ... -> librustc_driver ->
        libcore -> ... -> libstd

to

    librustc_lint -> librustc_driver -> libcore -> ... libstd

which is significantly faster, mainly due to avoiding the librustc build
itself.

The intention would be to move as much as possible of the infrastructure
into the crate too, but the plumbing is deeply intertwined with librustc
itself at the moment. Also, there are lints for which diagnostics are
registered directly in the compiler code, not in their own crate
traversal, and their definitions have to remain in librustc.

This is a [breaking-change] for direct users of the compiler APIs:
callers of `rustc::session::build_session` or
`rustc::session::build_session_` need to manually call
`rustc_lint::register_builtins` on their return value.

This should make #22206 easier.

mk/crates.mk

@@ -54,7 +54,7 @@ TARGET_CRATES := libc std flate arena term \
                  log graphviz core rbml alloc \
                  unicode rustc_bitflags
 RUSTC_CRATES := rustc rustc_typeck rustc_borrowck rustc_resolve rustc_driver \
-                rustc_trans rustc_back rustc_llvm rustc_privacy
+                rustc_trans rustc_back rustc_llvm rustc_privacy rustc_lint
 HOST_CRATES := syntax $(RUSTC_CRATES) rustdoc fmt_macros
 CRATES := $(TARGET_CRATES) $(HOST_CRATES)
 TOOLS := compiletest rustdoc rustc rustbook
@@ -70,20 +70,21 @@ DEPS_graphviz := std
 DEPS_syntax := std term serialize log fmt_macros arena libc
 DEPS_rustc_driver := arena flate getopts graphviz libc rustc rustc_back rustc_borrowck \
                      rustc_typeck rustc_resolve log syntax serialize rustc_llvm \
-		     rustc_trans rustc_privacy
+		     rustc_trans rustc_privacy rustc_lint
 
 DEPS_rustc_trans := arena flate getopts graphviz libc rustc rustc_back \
 	                log syntax serialize rustc_llvm
 DEPS_rustc_typeck := rustc syntax
 DEPS_rustc_borrowck := rustc log graphviz syntax
 DEPS_rustc_resolve := rustc log syntax
 DEPS_rustc_privacy := rustc log syntax
+DEPS_rustc_lint := rustc log syntax
 DEPS_rustc := syntax flate arena serialize getopts rbml \
               log graphviz rustc_llvm rustc_back
 DEPS_rustc_llvm := native:rustllvm libc std
 DEPS_rustc_back := std syntax rustc_llvm flate log libc
 DEPS_rustdoc := rustc rustc_driver native:hoedown serialize getopts \
-                test
+                test rustc_lint
 DEPS_rustc_bitflags := core
 DEPS_flate := std native:miniz
 DEPS_arena := std
@@ -128,11 +129,13 @@ DOC_CRATES := $(filter-out rustc, \
               $(filter-out rustc_resolve, \
               $(filter-out rustc_driver, \
               $(filter-out rustc_privacy, \
+              $(filter-out rustc_lint, \
               $(filter-out log, \
               $(filter-out getopts, \
-              $(filter-out syntax, $(CRATES)))))))))))
+              $(filter-out syntax, $(CRATES))))))))))))
 COMPILER_DOC_CRATES := rustc rustc_trans rustc_borrowck rustc_resolve \
-                       rustc_typeck rustc_driver syntax rustc_privacy
+                       rustc_typeck rustc_driver syntax rustc_privacy \
+                       rustc_lint
 
 # This macro creates some simple definitions for each crate being built, just
 # some munging of all of the parameters above.

mk/tests.mk

@@ -21,7 +21,7 @@ $(eval $(call RUST_CRATE,coretest))
 
 TEST_TARGET_CRATES = $(filter-out core unicode,$(TARGET_CRATES)) coretest
 TEST_DOC_CRATES = $(DOC_CRATES)
-TEST_HOST_CRATES = $(filter-out rustc_typeck rustc_borrowck rustc_resolve rustc_trans,\
+TEST_HOST_CRATES = $(filter-out rustc_typeck rustc_borrowck rustc_resolve rustc_trans rustc_lint,\
                      $(HOST_CRATES))
 TEST_CRATES = $(TEST_TARGET_CRATES) $(TEST_HOST_CRATES)
 

src/librustc/lib.rs

@@ -39,7 +39,6 @@
 #![feature(unsafe_destructor)]
 #![feature(staged_api)]
 #![feature(std_misc)]
-#![feature(unicode)]
 #![feature(os)]
 #![cfg_attr(test, feature(test))]