Merge #2379

2379: fix metal build r=grovesNL a=stuartcarnie

Fixes metal compilation issue:

    metallib: Invalid bitcode file!


PR checklist:
- [ ] `make` succeeds (on *nix)
    - a few failures due to rust-lang/rust#52801
- [x] `make reftests` succeeds
- [x] tested examples with the following backends: **metal**
- [x] `rustfmt` run on changed code

Co-authored-by: Stuart Carnie <[email protected]>

Author: bors[bot]

src/backend/metal/build.rs

@@ -55,7 +55,7 @@ fn main() {
         out_path.set_extension("air");
 
         let status = Command::new("xcrun")
-            .args(&["-sdk", sdk_name, "metal"])
+            .args(&["-sdk", sdk_name, "metal", "-c"])
             .arg(shader_path.as_os_str())
             .arg("-o")
             .arg(out_path.as_os_str())

src/backend/metal/shaders/blit.metal

@@ -1,4 +1,4 @@
-#include "macros.metal"
+#include "macros.h"
 #include <metal_stdlib>
 using namespace metal;
 

src/backend/metal/shaders/clear.metal

@@ -1,4 +1,4 @@
-#include "macros.metal"
+#include "macros.h"
 #include <metal_stdlib>
 using namespace metal;