Backport LLVM apfloat commit to rustc_apfloat

Backports LLVM commit: e34bd1e0b0

Fixes #69532

src/test/ui/issues/issue-69532.rs

@@ -0,0 +1,24 @@
+// run-pass
+#![feature(const_fn_transmute)]
+
+const fn make_nans() -> (f64, f64, f32, f32) {
+    let nan1: f64 = unsafe { std::mem::transmute(0x7FF0_0001_0000_0001u64) };
+    let nan2: f64 = unsafe { std::mem::transmute(0x7FF0_0000_0000_0001u64) };
+
+    let nan1_32 = nan1 as f32;
+    let nan2_32 = nan2 as f32;
+
+    (nan1, nan2, nan1_32, nan2_32)
+}
+
+static NANS: (f64, f64, f32, f32) = make_nans();
+
+fn main() {
+    let (nan1, nan2, nan1_32, nan2_32) = NANS;
+
+    assert!(nan1.is_nan());
+    assert!(nan2.is_nan());
+
+    assert!(nan1_32.is_nan());
+    assert!(nan2_32.is_nan());
+}