Include current_exe in hash for linker wrapper path

Ensures that unique linker wrapper scripts are generated even when
current_exe is different. Fixes an issue with concurrent builds driven
through maturin.

Closes #318.

src/zig.rs

@@ -1368,14 +1368,20 @@ pub fn prepare_zig_linker(target: &str) -> Result<ZigWrapper> {
         }
     }
 
+    let current_exe = if let Ok(exe) = env::var("CARGO_BIN_EXE_cargo-zigbuild") {
+        PathBuf::from(exe)
+    } else {
+        env::current_exe()?
+    };
     let cc_args_str = cc_args.join(" ");
-    let hash = crc::Crc::<u16>::new(&crc::CRC_16_IBM_SDLC).checksum(cc_args_str.as_bytes());
+    let hash_input = current_exe.display().to_string() + &cc_args_str;
+    let hash = crc::Crc::<u16>::new(&crc::CRC_16_IBM_SDLC).checksum(hash_input.as_bytes());
     let zig_cc = zig_linker_dir.join(format!("zigcc-{file_target}-{:x}.{file_ext}", hash));
     let zig_cxx = zig_linker_dir.join(format!("zigcxx-{file_target}-{:x}.{file_ext}", hash));
     let zig_ranlib = zig_linker_dir.join(format!("zigranlib.{file_ext}"));
-    write_linker_wrapper(&zig_cc, "cc", &cc_args_str)?;
-    write_linker_wrapper(&zig_cxx, "c++", &cc_args_str)?;
-    write_linker_wrapper(&zig_ranlib, "ranlib", "")?;
+    write_linker_wrapper(&current_exe, &zig_cc, "cc", &cc_args_str)?;
+    write_linker_wrapper(&current_exe, &zig_cxx, "c++", &cc_args_str)?;
+    write_linker_wrapper(&current_exe, &zig_ranlib, "ranlib", "")?;
 
     let exe_ext = if cfg!(windows) { ".exe" } else { "" };
     let zig_ar = zig_linker_dir.join(format!("ar{exe_ext}"));
@@ -1424,13 +1430,13 @@ fn symlink_wrapper(target: &Path) -> Result<()> {
 
 /// Write a zig cc wrapper batch script for unix
 #[cfg(target_family = "unix")]
-fn write_linker_wrapper(path: &Path, command: &str, args: &str) -> Result<()> {
+fn write_linker_wrapper(
+    current_exe: &PathBuf,
+    path: &Path,
+    command: &str,
+    args: &str,
+) -> Result<()> {
     let mut buf = Vec::<u8>::new();
-    let current_exe = if let Ok(exe) = env::var("CARGO_BIN_EXE_cargo-zigbuild") {
-        PathBuf::from(exe)
-    } else {
-        env::current_exe()?
-    };
     writeln!(&mut buf, "#!/bin/sh")?;
     writeln!(
         &mut buf,
@@ -1458,13 +1464,13 @@ fn write_linker_wrapper(path: &Path, command: &str, args: &str) -> Result<()> {
 
 /// Write a zig cc wrapper batch script for windows
 #[cfg(not(target_family = "unix"))]
-fn write_linker_wrapper(path: &Path, command: &str, args: &str) -> Result<()> {
+fn write_linker_wrapper(
+    current_exe: &PathBuf,
+    path: &Path,
+    command: &str,
+    args: &str,
+) -> Result<()> {
     let mut buf = Vec::<u8>::new();
-    let current_exe = if let Ok(exe) = env::var("CARGO_BIN_EXE_cargo-zigbuild") {
-        PathBuf::from(exe)
-    } else {
-        env::current_exe()?
-    };
     let current_exe = if is_mingw_shell() {
         current_exe.to_slash_lossy().to_string()
     } else {