Don't build out of line atomics support code for uefi

llvm/llvm-project#116706 added Windows
support to cpu_model. Compiling for UEFI also goes through that
code path, because we treat it as a windows target. However,
including windows.h is not actually going to work (and the used
API would not be available in an UEFI environment).

Disable building of cpu_model on UEFI to fix this.

Author: nikic

build.rs

@@ -644,9 +644,10 @@ mod c {
 
         // Include out-of-line atomics for aarch64, which are all generated by supplying different
         // sets of flags to the same source file.
-        // Note: Out-of-line aarch64 atomics are not supported by the msvc toolchain (#430).
+        // Note: Out-of-line aarch64 atomics are not supported by the msvc toolchain (#430) and
+        // on uefi.
         let src_dir = root.join("lib/builtins");
-        if target.arch == "aarch64" && target.env != "msvc" {
+        if target.arch == "aarch64" && target.env != "msvc" && target.os != "uefi" {
             // See below for why we're building these as separate libraries.
             build_aarch64_out_of_line_atomics_libraries(&src_dir, cfg);