Fix build for most binaries on musl.

m4/src/macros/builtin.rs

@@ -785,7 +785,7 @@ fn mkstemp(mut template: Vec<u8>) -> Result<Vec<u8>> {
     // SAFETY: According to https://man7.org/linux/man-pages/man3/mkstemp.3.html it seems like this is correct.
     let file_descriptor = unsafe {
         // Docs: https://pubs.opengroup.org/onlinepubs/009604499/functions/mkstemp.html
-        libc::mkstemp(template_pointer as *mut i8)
+        libc::mkstemp(template_pointer as *mut libc::c_char)
     };
     if file_descriptor < 0 {
         let e = errno::errno();

tree/mkfifo.rs

@@ -31,7 +31,12 @@ fn do_mkfifo(filename: &str, mode: &ChmodMode) -> io::Result<()> {
         ChmodMode::Symbolic(sym) => modestr::mutate(0o666, false, sym),
     };
 
-    let res = unsafe { libc::mkfifo(filename.as_ptr() as *const i8, mode_val as libc::mode_t) };
+    let res = unsafe {
+        libc::mkfifo(
+            filename.as_ptr() as *const libc::c_char,
+            mode_val as libc::mode_t,
+        )
+    };
     if res < 0 {
         return Err(io::Error::last_os_error());
     }

tree/touch.rs

@@ -139,7 +139,7 @@ fn parse_tm_ref_file(filename: &str) -> Result<DateTime<Utc>, Box<dyn std::error
 fn touch_file_new(time: libc::time_t, filename: &str) -> Result<(), Box<dyn std::error::Error>> {
     // open file for writing, creating if necessary
     let flags = libc::O_CREAT | libc::O_WRONLY | libc::O_TRUNC;
-    let fd = unsafe { libc::open(filename.as_ptr() as *const i8, flags, 0o666) };
+    let fd = unsafe { libc::open(filename.as_ptr() as *const libc::c_char, flags, 0o666) };
     if fd < 0 {
         return Err("Failed to open file".into());
     }
@@ -219,7 +219,7 @@ fn touch_file_existing(
     ];
 
     // set file times
-    if unsafe { libc::utimes(filename.as_ptr() as *const i8, times.as_ptr()) } < 0 {
+    if unsafe { libc::utimes(filename.as_ptr() as *const libc::c_char, times.as_ptr()) } < 0 {
         return Err("Failed to change file times".into());
     }