fix spirv-builder with default-features = false failing to compile

Author: Firestar99

crates/spirv-builder/src/lib.rs

@@ -981,12 +981,17 @@ fn invoke_rustc(builder: &SpirvBuilder) -> Result<PathBuf, SpirvBuilderError> {
     // target_spec jsons, some later version requires them, some earlier
     // version fails with them (notably our 0.9.0 release)
     if toolchain_rustc_version >= Version::new(1, 76, 0) {
-        let path = builder.path_to_target_spec.clone();
-        let path = if cfg!(feature = "include_target_specs") {
-            path.unwrap_or_else(|| PathBuf::from(format!("{TARGET_SPEC_DIR_PATH}/{target}.json")))
-        } else {
-            path.ok_or(SpirvBuilderError::MissingTargetSpec)?
-        };
+        let path_opt = builder.path_to_target_spec.clone();
+        let path;
+        #[cfg(feature = "include_target_specs")]
+        {
+            path = path_opt
+                .unwrap_or_else(|| PathBuf::from(format!("{TARGET_SPEC_DIR_PATH}/{target}.json")));
+        }
+        #[cfg(not(feature = "include_target_specs"))]
+        {
+            path = path_opt.ok_or(SpirvBuilderError::MissingTargetSpec)?;
+        }
         cargo.arg("--target").arg(path);
     } else {
         cargo.arg("--target").arg(target);