Disable libm on x86 without sse2

In <#594>, symbols
for the Rust port of libm were made always weakly available. This seems
to be causing problems on platforms with ABI issues, as explained at
<rust-lang/rust#125016 (comment)>.

Disable Rust libm on x86 without sse2 to mitigate this.

Author: tgross35

src/lib.rs

@@ -47,6 +47,9 @@ mod macros;
 pub mod float;
 pub mod int;
 
+// Disabled on x86 without sse2 due to ABI issues
+// <https://github.com/rust-lang/rust/issues/114479>
+#[cfg(not(all(target_arch = "x86", not(target_feature = "sse2"))))]
 pub mod math;
 pub mod mem;