Use rustdoc output to create a list of public API

Rather than collecting a list of file names in `libm-test/build.rs`,
just use a script to parse rustdoc's JSON output.

library/compiler-builtins/libm/crates/libm-test/src/lib.rs

@@ -23,9 +23,6 @@ pub use test_traits::{CheckOutput, GenerateInput, Hex, TupleCall};
 /// propagate.
 pub type TestResult<T = (), E = anyhow::Error> = Result<T, E>;
 
-// List of all files present in libm's source
-include!(concat!(env!("OUT_DIR"), "/all_files.rs"));
-
 /// True if `EMULATED` is set and nonempty. Used to determine how many iterations to run.
 pub const fn emulated() -> bool {
     match option_env!("EMULATED") {
@@ -34,3 +31,12 @@ pub const fn emulated() -> bool {
         Some(_) => true,
     }
 }
+
+/// True if `CI` is set and nonempty.
+pub const fn ci() -> bool {
+    match option_env!("CI") {
+        Some(s) if s.is_empty() => false,
+        None => false,
+        Some(_) => true,
+    }
+}