fix(build.rs): don't recompile build script if features change

Signed-off-by: Martin Kröning <[email protected]>

build.rs

@@ -3,14 +3,17 @@ use std::env;
 fn main() -> Result<(), String> {
 	let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
 	let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
+	let fc = env::var_os("CARGO_FEATURE_FC").is_some();
 
 	if target_arch == "x86_64" && target_os == "none" {
 		let mut nasm = nasm_rs::Build::new();
 
-		#[cfg(feature = "fc")]
-		nasm.file("src/arch/x86_64/entry_fc.asm");
-		#[cfg(not(feature = "fc"))]
-		nasm.file("src/arch/x86_64/entry.asm");
+		let entry = if fc {
+			"src/arch/x86_64/entry_fc.asm"
+		} else {
+			"src/arch/x86_64/entry.asm"
+		};
+		nasm.file(entry);
 		let objects = nasm.compile_objects()?;
 
 		let mut cc = cc::Build::new();