std: Remove internal definitions of `cfg_if!` macro

This is duplicated in a few locations throughout the sysroot to work
around issues with not exporting a macro in libstd but still wanting it
available to sysroot crates to define blocks. Nowadays though we can
simply depend on the `cfg-if` crate on crates.io, allowing us to use it
from there!

3 files changed, 2 insertions, 39 deletions

diff --git a/src/libpanic_unwind/Cargo.toml b/src/libpanic_unwind/Cargo.toml
index 1b3901ac11a..47cd09f1b05 100644
--- a/src/libpanic_unwind/Cargo.toml
+++ b/src/libpanic_unwind/Cargo.toml
@@ -16,3 +16,4 @@ core = { path = "../libcore" }
 libc = { version = "0.2", default-features = false }
 unwind = { path = "../libunwind" }
 compiler_builtins = "0.1.0"
+cfg-if = "0.1.8"
diff --git a/src/libpanic_unwind/lib.rs b/src/libpanic_unwind/lib.rs
index 72ddafb420c..2bb9ce6ab22 100644
--- a/src/libpanic_unwind/lib.rs
+++ b/src/libpanic_unwind/lib.rs
@@ -38,10 +38,7 @@ use core::mem;
 use core::raw;
 use core::panic::BoxMeUp;
 
-#[macro_use]
-mod macros;
-
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(target_os = "emscripten")] {
         #[path = "emcc.rs"]
         mod imp;
diff --git a/src/libpanic_unwind/macros.rs b/src/libpanic_unwind/macros.rs
deleted file mode 100644
index 659e977285e..00000000000
--- a/src/libpanic_unwind/macros.rs
+++ /dev/null
@@ -1,35 +0,0 @@
-/// A macro for defining `#[cfg]` if-else statements.
-///
-/// This is similar to the `if/elif` C preprocessor macro by allowing definition
-/// of a cascade of `#[cfg]` cases, emitting the implementation which matches
-/// first.
-///
-/// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code
-/// without having to rewrite each clause multiple times.
-macro_rules! cfg_if {
-    ($(
-        if #[cfg($($meta:meta),*)] { $($it:item)* }
-    ) else * else {
-        $($it2:item)*
-    }) => {
-        __cfg_if_items! {
-            () ;
-            $( ( ($($meta),*) ($($it)*) ), )*
-            ( () ($($it2)*) ),
-        }
-    }
-}
-
-macro_rules! __cfg_if_items {
-    (($($not:meta,)*) ; ) => {};
-    (($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => {
-        __cfg_if_apply! { cfg(all(not(any($($not),*)), $($m,)*)), $($it)* }
-        __cfg_if_items! { ($($not,)* $($m,)*) ; $($rest)* }
-    }
-}
-
-macro_rules! __cfg_if_apply {
-    ($m:meta, $($it:item)*) => {
-        $(#[$m] $it)*
-    }
-}