Move the force_eval! macro into the math module

This fixes the cross-inclusion into the compiler builtins

library/compiler-builtins/libm/src/math/mod.rs

@@ -1,3 +1,9 @@
+macro_rules! force_eval {
+    ($e:expr) => {
+        unsafe { ::core::ptr::read_volatile(&$e); }
+    }
+}
+
 mod fabs;
 mod fabsf;
 mod fmodf;