Actually enable the amdgpu component if present.

Author: DiamondLovesYou

src/librustc_llvm/build.rs

@@ -81,7 +81,7 @@ fn main() {
     let is_crossed = target != host;
 
     let mut optional_components =
-        vec!["x86", "arm", "aarch64", "mips", "powerpc",
+        vec!["x86", "arm", "aarch64", "amdgpu", "mips", "powerpc",
              "systemz", "jsbackend", "webassembly", "msp430", "sparc", "nvptx"];
 
     let mut version_cmd = Command::new(&llvm_config);