platform-host: fix musl version detection bug

I'm not quite sure how this was every working before. It's possible
it has never worked, but that our other methods of OS detection were
working.

In any case, empirically, it seems that the version number components
for musl can be a single digit.

Fixes #1427

crates/platform-host/src/linux.rs

@@ -168,7 +168,7 @@ fn detect_musl_version(ld_path: impl AsRef<Path>) -> Result<Os, PlatformError> {
 
 fn musl_ld_output_to_version(kind: &str, output: &[u8]) -> Result<Os, PlatformError> {
     static RE: Lazy<Regex> =
-        Lazy::new(|| Regex::new(r"Version ([0-9]{2,4})\.([0-9]{2,4})").unwrap());
+        Lazy::new(|| Regex::new(r"Version ([0-9]{1,4})\.([0-9]{1,4})").unwrap());
 
     let output = std::str::from_utf8(output).map_err(|err| {
         PlatformError::OsVersionDetectionError(format!("failed to parse {kind} as UTF-8: {err}"))
@@ -180,7 +180,7 @@ fn musl_ld_output_to_version(kind: &str, output: &[u8]) -> Result<Os, PlatformEr
             RE.as_str(),
         )));
     };
-    // OK since we are guaranteed to have between 2 and 4 ASCII digits and the
+    // OK since we are guaranteed to have between 1 and 4 ASCII digits and the
     // maximum possible value, 9999, fits into a u16.
     let major = major.parse().expect("valid major version");
     let minor = minor.parse().expect("valid minor version");
@@ -242,4 +242,21 @@ Written by Roland McGrath and Ulrich Drepper.",
             }
         );
     }
+
+    #[test]
+    fn parse_musl_ld_output() {
+        // This output was generated by running `/lib/ld-musl-x86_64.so.1`
+        // in an Alpine Docker image. The Alpine version:
+        //
+        // # cat /etc/alpine-release
+        // 3.19.1
+        let output = b"\
+musl libc (x86_64)
+Version 1.2.4_git20230717
+Dynamic Program Loader
+Usage: /lib/ld-musl-x86_64.so.1 [options] [--] pathname [args]\
+        ";
+        let got = musl_ld_output_to_version("stderr", output).unwrap();
+        assert_eq!(got, Os::Musllinux { major: 1, minor: 2 });
+    }
 }