Auto merge of #38482 - est31:i128, r=eddyb

i128 and u128 support

Brings i128 and u128 support to nightly rust, behind a feature flag. The goal of this PR is to do the bulk of the work for 128 bit integer support. Smaller but just as tricky features needed for stabilisation like 128 bit enum discriminants are left for future PRs.

Rebased version of  #37900, which in turn was a rebase + improvement of #35954 . Sadly I couldn't reopen #37900 due to github. There goes my premium position in the homu queue...

[plugin-breaking-change]

cc #35118 (tracking issue)

mk/crates.mk

@@ -54,7 +54,7 @@ TARGET_CRATES := libc std term \
                  compiler_builtins core alloc \
                  std_unicode rustc_bitflags \
 		 alloc_system alloc_jemalloc \
-		 panic_abort panic_unwind unwind
+		 panic_abort panic_unwind unwind rustc_i128
 RUSTC_CRATES := rustc rustc_typeck rustc_mir rustc_borrowck rustc_resolve rustc_driver \
                 rustc_trans rustc_back rustc_llvm rustc_privacy rustc_lint \
                 rustc_data_structures rustc_platform_intrinsics rustc_errors \
@@ -92,23 +92,26 @@ DEPS_getopts := std
 DEPS_graphviz := std
 DEPS_log := std
 DEPS_num := std
-DEPS_serialize := std log
+DEPS_serialize := std log rustc_i128
 DEPS_term := std
 DEPS_test := std getopts term native:rust_test_helpers
+DEPS_rustc_i128 = std
 
-DEPS_syntax := std term serialize log arena libc rustc_bitflags std_unicode rustc_errors syntax_pos rustc_data_structures
+DEPS_syntax := std term serialize log arena libc rustc_bitflags std_unicode rustc_errors \
+			syntax_pos rustc_data_structures rustc_i128
 DEPS_syntax_ext := syntax syntax_pos rustc_errors fmt_macros proc_macro
+DEPS_proc_macro := syntax syntax_pos rustc_plugin log
 DEPS_syntax_pos := serialize
 DEPS_proc_macro_tokens := syntax syntax_pos log
 DEPS_proc_macro_plugin := syntax syntax_pos rustc_plugin log proc_macro_tokens
 
-DEPS_rustc_const_math := std syntax log serialize
+DEPS_rustc_const_math := std syntax log serialize rustc_i128
 DEPS_rustc_const_eval := rustc_const_math rustc syntax log serialize \
-			     rustc_back graphviz syntax_pos
+			     rustc_back graphviz syntax_pos rustc_i128
 
 DEPS_rustc := syntax fmt_macros flate arena serialize getopts \
               log graphviz rustc_llvm rustc_back rustc_data_structures\
-	      rustc_const_math syntax_pos rustc_errors
+	      rustc_const_math syntax_pos rustc_errors rustc_i128
 DEPS_rustc_back := std syntax flate log libc
 DEPS_rustc_borrowck := rustc log graphviz syntax syntax_pos rustc_errors rustc_mir
 DEPS_rustc_data_structures := std log serialize libc
@@ -119,19 +122,20 @@ DEPS_rustc_driver := arena flate getopts graphviz libc rustc rustc_back rustc_bo
                      rustc_passes rustc_save_analysis rustc_const_eval \
                      rustc_incremental syntax_pos rustc_errors proc_macro rustc_data_structures
 DEPS_rustc_errors := log libc serialize syntax_pos
-DEPS_rustc_lint := rustc log syntax syntax_pos rustc_const_eval
+DEPS_rustc_lint := rustc log syntax syntax_pos rustc_const_eval rustc_i128
 DEPS_rustc_llvm := native:rustllvm libc std rustc_bitflags
 DEPS_proc_macro := std syntax
 DEPS_rustc_metadata := rustc syntax syntax_pos rustc_errors rustc_const_math \
-			proc_macro syntax_ext
+			proc_macro syntax_ext rustc_i128
 DEPS_rustc_passes := syntax syntax_pos rustc core rustc_const_eval rustc_errors
-DEPS_rustc_mir := rustc syntax syntax_pos rustc_const_math rustc_const_eval rustc_bitflags
+DEPS_rustc_mir := rustc syntax syntax_pos rustc_const_math rustc_const_eval rustc_bitflags \
+					rustc_i128
 DEPS_rustc_resolve := arena rustc log syntax syntax_pos rustc_errors
 DEPS_rustc_platform_intrinsics := std
 DEPS_rustc_plugin := rustc rustc_metadata syntax syntax_pos rustc_errors
 DEPS_rustc_privacy := rustc log syntax syntax_pos
 DEPS_rustc_trans := arena flate getopts graphviz libc rustc rustc_back \
-                    log syntax serialize rustc_llvm rustc_platform_intrinsics \
+                    log syntax serialize rustc_llvm rustc_platform_intrinsics rustc_i128 \
                     rustc_const_math rustc_const_eval rustc_incremental rustc_errors syntax_pos
 DEPS_rustc_incremental := rustc syntax_pos serialize rustc_data_structures
 DEPS_rustc_save_analysis := rustc log syntax syntax_pos serialize
@@ -159,6 +163,7 @@ ONLY_RLIB_alloc := 1
 ONLY_RLIB_rand := 1
 ONLY_RLIB_collections := 1
 ONLY_RLIB_std_unicode := 1
+ONLY_RLIB_rustc_i128 := 1
 ONLY_RLIB_rustc_bitflags := 1
 ONLY_RLIB_alloc_system := 1
 ONLY_RLIB_alloc_jemalloc := 1